The file handling system changes drastically in 3.0 for multi-site, (not for normal single-site), so expect some weirdness there if you try to go that route. Took me a while to get the hang of it.

This doesn't affect the media-library view of it though, which has gotten much better in recent versions and is very useful now. I wish we could dump the flash uploader though. It's definitely a problem on some systems. Perhaps HTML5 adoption will help that.