My only complaint is load times and the static nature of the UI now. I'd really like to be able to expand/contract any of the sidebar headings. Being that I have a lot of playlists, I get scrollbars in my source list, which I absolutely abhor.
Other than that... not bad. Not bad at all. I really like the new logo, too, not quite as much as iTunes 1's, but it's a lot more refined than iTunes 2's. This is probably one of the better iTunes releases, I think. About on par with 4.
I'm so happy to see the album view incorporated. The Cover Flow view is nice, but I'll probably stick to running iTunes + Full screened CoverFlow for that feature. Leopard, here we come. 😀