Be sure to read about these startups which failed trying to do something similar:

Verfiable: http://stuartroseman.com/post/619953720/out-with-the-old-bus...

http://eagereyes.org/blog/2010/end-of-verifiable-com

Swivel: http://eagereyes.org/criticism/the-rise-and-fall-of-swivel

I guess the takeaway is that the business model is probably B2B, and you need to fulfill a real need.