Over the past 7 years using the different sites I've turned down 20 projects that I've been asked to bid on, and have only taken one when I was really in dire straits. You could probably make more on odesk than at mcdonalds, but you'll make 5-8x as much by building up a network on linkedin, and by posting your resume to craigslist once per week. I set my contracting rate on a sliding scale from $250/hour down to $125/hour based on commitment, project, and how much I like the guy I'm talking with. I manage to bill out 750-1250 hours per year depending on how much I care to work versus how much I desire to travel. I couldn't fathom managing to bill out at more than $35/hour on oDesk, and even then I would be considered expensive.
oDesk/elance/etc is where cheapskates who don't know what they want or how to ask for it go to get what they pay for from guys in India and Romania who don't know how to accomplish the work they're being paid to do.