Initial thoughts and observations:
1. It's 'Stack Overflow for the common (wo)man' with cash instead of reputation.
2. Alternative pitch: "99designs meets Yahoo Answers."
3. The top prize available at the moment awards $50.
4. The sign-up process could be a lot better. Prompting sign-up via twitter/Facebook, then prompting for a prizes.org-only username and password is an unusual approach.
5. 'Contest' creation is currently by invitation only.
6. Answers you give that are accepted become the IP of the person who awarded the prize. (http://prizes.org/faq )
7. I'm not yet convinced that there's a huge market for paid responses when the Stack Exchange network and Quora both offer large userbases who give their time to answer questions for free.