I like this idea. I personally think you are charging too little though. I know you want to make it affordable even for students but I feel that may only open it up for lower level programmers who are okay with working for low rates.

There is already a ton of help available online for low prices or free. I would like to see a service that focuses on instant help like this but with very experienced developers. I would have no problem paying over $60/hr or even a $100+ per hour for a guarantee that my problem will be solved. I would even fork out that kind of money for my employees to use a service like that. Something that I can deposit a certain amount of money per month into my employees account wallet which they can use towards live support issues and it only gets deducted if the problem was solved.

I may not be the norm though so take what I say with a grain of salt ;)