The unified experience definitely is interesting. I definitely don’t listen to music on my TV, but I do listen to music and watch pure video content on YouTube.
The other big thing working in YouTube’s favour is that (basically) everything is uploaded by fans. It lacks the long-tale of crap that comes through labels & digital distributors to Rdio / Spotify / MediaNet but instead has the music that people care about enough to attach to a crappy montage & upload.
Grooveshark is a sad case because if they hadn’t set themselves up with an idiotic piracy happy attitude they might have been able to get somewhere. They seem to have the juvenile “if we really want to do it then it *must* be lega” attitude that I’m used to from teenagers and stoners.
The best catalogue and cleanest metadata is of course on private bittorrent trackers where the community cares about music and nobody is trying to make a buck.