I'm doing a (tangentially related) twist on this sort of thing, so I'll ask you the questions that haunted me for months until I could answer them about my own project:

Who's going to use this?

I mean, what's the intersection of people that are computer-articulate enough to know what to ask for ("convert this file for me"), but don't know how to do it, and/or are willing to spend the extra minute or two to post and manage the "favor"? Especially when "know how to do it" means "google for the free web app that does it"?

And who is going to spend their time doing these favors, with no reward except some ethereal concept of "points" that can only be redeemed for doing the things I can already easily do myself (see above)? Realize that you're competing for attention from facebook/twitter/HN. And MTurk, which actually pays.

http://www.minutefavors.com/favors/8 Is is legal to do that?

So what prevents people from creating new accounts and acquiring new favors ? May be you should keep a mobile number verification....

I think you might want to work on 'faking it until you make it' by pre-seeding a ton of favors to ask of people.

I've heard of this place that's been around for decades where you can log in, ask questions and quickly get answers for free in real time from knowledgeable people. I believe it's called IRC.

Mechanical Turk is a marketplace; are you planning to provide the opportunity for people to purchase points in the future? Sounds more like Experts-Exchange meets StackExchange.

Have you considered allowing comments on favors? People might want to discuss solutions they've seen in the past or ask for clarification.

the newest favors are the same set as the oldest favors :)

jig.com in another bottle ?

My first thought: a new source for business ideas. Read through favors, see which ones popup the most, implement solution.