Wow this thread has been incredibly informative, thank you!
I used to be a member of Freelancer.com as a translator. Fortunately I didn't get any projects! I bid like crazy for a while but never got chosen; now I'm thankful for that :P
I'll just share that it took me about 5 days to unregister, because they don't let you just cancel your membership, you have to go through their terrible customer service reps. Once the request is made via email, they send you at least two lengthy emails stating the thousands of "benefits" of being a member, "why don't you reconsider", etc. I found this very annoying!