3.0 is awesome, I have a couple of small gripes but for the most part its a great update.
the main issues I personally have after a few gigs of using are:
1. the UI is all way too dark, did an outdoor gig and the screen was unusable until I inverted the screen colors on my mac
2. there is not a way to always have your full collection live if you also browse playlists like in the old version, so now if I want to search for a track quick i have to scroll all the way to the top of click a shortcut to the left and then search whereas in 2.x I could simply hit CTRL+F no matter what I was doing
3. after you search the search results do not clear if you click into a playlist so you panic thinking all the tracks were deleted, lol
4. they use a lot of wasted space in the palette views for album art, I don't use album art, they should let them be customizable
5. If you have a large library and a lot of playlists, the sync manager "checks playlists" every time and it takes 1-1.5 minutes before the sync actually starts, pretty annoying if you only update a few tracks and need to sync quick