I had used a freelance site vWorker.com for 2 years and shared my experience as a blog post. . In brief, I didn't like the ineffective arbitration process of this freelance site. You can share your experience from various freelance sites so that this thread will become a reference place for knowing/analyzing any freelance site.
I'm a member at Freelancer ex GAF since 2004 and i have 314 Reviews as a Freelancer and i earn my living this way Yea Arbitration isn't perfect anywere trust me but in the long term i'm very happy with them and they have options no other site have (Gold Member + Payment methods ...)
I've tried all the major freelance sites and the best experience has been with vWorker. Was particularly disappointed with arbitration on elance unfortunately. I've used my experiences to create my own web services marketplace (just launched) and you guys are welcome to list what you can offer (see signature)