Well, .biz will be easier to optimize and get page ranking quicker than some of the other extensions.
I would imagine lean.biz as either a weight loss products store and program information of some sort. Or a manufacturers website. Lean can be applied to many things. It's short it's one word, and it's a top level domain.
Lean.biz could sell food and products that are low in fat. One possibility is making it a business resource site the provides tools, techiniques and information on how to run your business lean and have more profitablity.
Could be used as a consulting site. What about selling only fresh lean meat? I think there are a lot of uses for it and it doesn't have to just mean lean and weight loss.
If you are serious about this name and really need some ideas, I'm the Idea Doc. I'd be happy to help you come up with a profitable idea for developing this.
Hope this helps.
