I started using Elance about a month ago and I've had pretty good luck so far.
I'm mostly interested in medical writing, but the first two jobs that I took were totally unrelated photo essay assignments. They paid $50 each for about half an hour of work, so great pay... but I mainly did them so my profile would reflect two completed jobs and thus look a bit more 'legit.' I'm now working on a bigger project through Elance, writing a continuing education course for an online company. It's a legit (albeit small) company and the pay is very fair.
I've definitely seen some things that looked like scams, but there are plenty of decent offerings if you look a bit.