Spike Wyatt, better known perhaps as Spike the Lobster or Scrawlbug has way more experience with bidding sites like Elance than I do. I tend to be suspicious of them; Spike has figured out how to use them to his own advantage. Take a look:
These three posts will give you a whole different look at bidding sites than you’ll get from me. In fact, they might even change my opinion just a bit.
Image from http://www.sxc.hu