The domain names of spammy websites are often very long and contain many hyphens. Those domain names often contain commercial high value keywords (the keywords for which you receive lots of spam messages that we don't want to mention here).
Spammy domains are often registered by people who own a very large number of domains. The more domains a person owns, the more likely it is that the quality of a single domain isn't high. Spammy domains are often very young and have a short registration period. Low quality domains also often use .info, .cc, .us and other cheap top level domains.
Spammy websites often have many keyword-stuffed sub domains.

Spammy websites often show very many ads. They also often contain high-commercial keywords. The keyword density and the keyword frequency on low quality websites is often very high.
Spammy websites often have duplicate content and content scraped from other websites. Low quality websites usually don't have unique content.
Low quality websites usually don't contain a privacy policy, a copyright notice page and "Contact us" page with a full address.

Spammy websites often have many links to other spam and low quality websites. Low quality websites aren't likely to have links from trusted sites.

Spammy website often use redirects (JavaScript, MetaRefresh, etc.) from landing pages. Spammy websites also often use cloaking. Of course, other spam elements such as hidden text also cause problems with search engines.

"[Google] introduced a search-within-search feature that lets users stay on Google to find pages on popular sites [...] The problem [...] is that when someone enters a term into that secondary search box, Google will display ads for competing sites, thereby profiting from ads it sells against the brand."

"If you entered long queries in a Google search box, you would notice that it's difficult to edit them because Google optimized the size of the box for short queries. Things have changed and now you can [enter] much bigger queries and Google will adjust the search box's size after you perform a search."

Google is testing Google Suggest like features on Google.com on some users. This feature is already implemented as a default on other non-U.S. based Google home pages. Both Yahoo and Ask.com already offer search suggestions as you type.

"For the past 10 years, most search engines have relied heavily on analyzing anchor text, links, and content to determine relevance, he said. Recently, research by the top search engines has looked at other signals, such as user clicks and engagement [...]"

"Perhaps you've heard about 'Negative SEO' or 'Google bowling,' where your competitors use spam techniques seemingly on your behalf to knock down your site. [...] Google has choices and we need to scream that they make some better ones."

"In February 2008 both Microsoft and Yahoo lost ground to Google, who continues to widen its lead. [...] Based on the latest comScore results, Yahoo doesn't look like Microsoft's silver bullet in the battle against Google."

"WOW, that is all I have to say. I am so impressed with the complete package of software that came with iBusinessPromoter and how easy it is to use.
Really it has taken my business services to a entire different level. The PDF reports are worth the cost of the software themselves. I look forward to all the new products that come available from Axandra."
Wade Wicklund, PerazimMedia.com

"IBP was very helpful when we optimized our website. The new version is perfect."
Carsten Scholz, www.GoFinance24.de

"Almost eight years ago, Yahoo decided to lend a little start-up a helping hand, featuring its search technology on the Yahoo home page and giving it money at a critical juncture. [...]
The start-up was Google, and Yahoo's generosity helped launch the most formidable competitor it had ever encountered."

"Google Ad Manager is one critical piece in creating the open network of networks where any site can take any ad and any marketer can advertise on any site. When that day arrives, we all become atoms that can attract to one molecule or another, no longer locked into one network."
Related: OpenX vs Google Ad Manager, Google’s Trojan Horse: let the free ad serving begin

"In what has to be one of the weirdest Q&As we've read in a long time, Google CEO Eric Schmidt tells Portfolio's Russ Mitchell that a Microsoft-Yahoo deal could 'break the internet.' Was he kidding? Apparently not."
Related: Microsoft, Yahoo execs finally meet, Yahoo showing signs of life, albeit too late

"The new strategy, unveiled along with a restructuring that will reduce Ask's work force by 8%, or about 40 jobs, is a retreat from efforts by former Ask management to broaden the search engine's audience beyond middle-American, predominantly female consumers, who have long made up its core."

"If you thought click fraud was bad, consider this: your Google AdWords, Yahoo! Search Marketing ads and Microsoft adCenter accounts are new targets for spyware applications, hackers and scam artists."

"European regulators plan to approve Google Inc.'s proposed $3.1 billion takeover of DoubleClick Inc. without conditions, rejecting complaints by Microsoft Corp. that the deal would hurt competition, according to three people with direct knowledge of the case."

Google now sometimes adds an additional search box in the search results that allows searches to search within a site. For example, you'll get the additional search box if you search Google.com for "amazon", "ny times" or "wikipedia":

"Former Google Product Manger, Steffen Mueller, has launched Topicle, a new search engine community. The service, which went live today, uses a model similar to that of Wikipedia, allowing anyone to contribute to the creation and enhancement of their own vertical"

"Google accounted for 66.44 percent of all U.S. searches in the four weeks ending February 23, 2008. Yahoo! Search, MSN Search and Ask.com each received 20.59, 6.95 and 4.16 percent respectively."

"Earlier this week, comScore released its January 2008 qSearch paid click report, which showed a 7% sequential decline vs. December ‘07, and a flat annual growth in paid clicks for Google. Moreover, the number of paid clicks per Google search query declined by 8% from December to January, suggesting that consumers are clicking less on search ads, possibly reflecting a weaker buying appetite."
Related: Google to ComScore: You owe us $15-billion, Google: the hollow echo of a click, Google housecleaning explains ad drop

"A recent report on Click Fraud suggests that the maximum number of invalid clicks on Pay Per Click ads originate from India. And this is not the first time - its widely believed there there exists a large 'work from home' crowd in India who want to generate 'quick cash' by clicking Google AdSense ads."

"Code-named 'Search Monkey,' the new open-source application programming interfaces (API) that Yahoo is slated to detail today will allow Web site owners to add information such as ratings and reviews, images, deep links and other data directly to the Yahoo Search results Web page."

"From January 2008 to February 2008, Google picked up 2.3 points of ad spend share. Google’s growth came at the expense of Yahoo (down 1.6 points), Microsoft (down 0.6 points), and Ask (down 0.1 points). [...]
Comparing February 2008 to February 2007, we did not observe evidence of an advertising or sales slow-down: median same-client Google ad-spend was up 22% year-over-year, and corresponding same-client resulting PPC sales were up 26%."

"Online search site Ask.com is not getting rid of its specialized search technology, a source familiar with the matter said on Friday, saying a blog report to that effect was incorrect."

"We're in the process of rolling out some changes to our crawling, indexing and ranking algorithms. While we expect the update will be completed soon, as you know, throughout this process you may see some ranking changes and page shuffling in the index."

There are many reasons why content is duplicated on more than one page, or why documents are very similar:

1. The content of a web page is available in different formats: web page, printable page, PDF, mobile phone page, etc.
2. The content of a web page is syndicated, for example news articles or blog posts.
3. The content management system (CMS) displays the same content in different locations. For example, an item might be listed in a "Size" category and in a "Color" category.
4. The website owner offers mirrors to make sure that a website does not slow down when many people want to access the same page at the same time.
5. Someone stole the contents of a web page to reproduce it on other websites.

To avoid showing the same content more than once in the search results, search engines try to detect these duplicate pages.

The patent application describes how Google tries to detect duplicate or near duplicate content at different web addresses. It seems that Google might combine several existing methods for detecting new duplicate content to identify more duplicates on the Internet.
The new patent application shows that Google is serious about detecting duplicate content issues. This new patent application is only the latest step in Google's attempts to detect duplicate content. For example, previous steps can be found here (PDF) and here.

It's hard to tell what Google will do when they find duplicate pages. There are many instances where duplicated content is used for a legitimate purpose.
If Google only removes the duplicate pages from the search results for a certain query that might be okay. If Google penalized duplicate pages by removing them completely from the index, Google might risk not being relevant for very specific queries and it also might penalize the wrong pages.
It's likely that Google will pick the web page with the best reputation and the best inbound links for the search results if it finds more than one page with the same content.