Web Sites for Freelancers – opinions

I’m trying word this so that it doesn’t turn into a commercial…

Has anyone an opinion about Web sites/services connecting freelancers with projects? I’d like to know good & bad experiences, are they worth it, has your company posted a gig, how did it turn out? Did the bids go so low that the freelancer had no hope of completing the project in the black?

I’m also exploring the option of using subcontractors to farm out portions of projects when geography is an issue or if I ever bite offmore than I can chew.