I don't like .mobi because the web was designed as a device-independent medium and .mobi goes counter that (IMO great) concept. Device-independent design does not mean you can't serve tailored content to the browser using content negotiation techniques. I mean, come on, do you want a .handi for websites that are certified for impaired people
IMO the mobile Internet boils down to an accessibility issue.
A separate extension further isolates the struggling mobile web.
The distinction between desktop and mobile has already blurred and technology continues to evolve at a rapid pace, making the justification for a separate TLD even more obsolete.
Last but not least I also think it's unbrandable.