You may find http://www.interviewzen.com/ useful. It's a hiring tool I'm building around the idea that you can tell a lot about someone's coding ability by seeing them in action.
Ha! I had this exact same idea not long ago, that's interesting. Have you talked to (potential) customers? I've had multiple times questions like "what's the advantage over google docs/screen sharing?" (which is free).
Feedback has been very positive so far - customers are finding it makes the initial screening process much easier. One advantage over Google Docs is the ability to do time-shifted interviews, making it a good first filter for job postings.
Feel free to drop me a mail and we can chat further.
