The only thing that bugs me, is on iOS, when I load the music app (that's basically iTunes for iOS, right?) it shows a blank page until it can connect to the their servers to grab some data. It doesn't have a problem if I'm on wifi or a fast connection, but I'm often in places where my service is shit, and I get a white screen and can't pick what music I want to listen to. My workaround is to pull the menu up from the bottom of the screen and just hit "play" and then it usually works.
But iTunes itself, I do like.