from what I've seen in the Fullscreen library, it's a pretty mixed bag. The search function is pretty bad to be honest, but I sent an e-mail and they said they are working on improving it. They have a couple of good house/dubstep beats and I've found a few other tracks. The hardest thing is that the people that are uploading content don't keep it consistent. So sometimes there's an author, and sometimes not. The search function is basically by genre with no option to search by artist. Then you have hundreds of pages to wade through which can be time consuming.
So with that said....I still actually like having royalty free music. It's a bit of a pain at this current stage, but I think with a new layout it could be vastly improved and really empower creators.
