I personally recommend everyone to not use Freelancer.com. I learned in this thread that they also bought vWorker, and I am not surprised to read that it has turned for the worse after being acquired.
In short, they steal from both the freelancers and the outsourcers - stories aplenty about this [1]. I only know about these stories because I started looking into them after being bamboozled myself, luckily for only a small amount, which would have been larger had I not managed to cancel the additional payments Freelancer.com had booked against my credit card without permission. This was my experience as an outsourcer, apparently the freelancers have it far worse.
Elance on the other hand has seen more than $20k of my business and will continue to in the foreseeable future. Have not had experience with the other services (there's a strong lock-in effect in this market because your job history itself becomes a valuable thing).