Here's a cool new feature in iTunes 10 that we haven't mentioned yet: when listening to any song in your library, you can double click on the album art window in the lower left hand corner to detach it from the main window and see it full size. That's not new -- you could get a closer look at the art in previous versions of iTunes. But what is new is that when you mouse over that detached art, you now get full QuickTime-style controls for your tracks. You can then minimize the main window (using those weirdly-aligned buttons, of course), and then just control the music directly from that square widget (which can also be resized any way you want).
Pretty neat, and somewhat hard to find if you don't usually zoom in to see your album art full size. This
