I installed iTunes 10 over the weekend and found one major annoyance.
Apple moved the window buttons to the side of the window, unnecessarily. It’s almost distracting, but easily changed.
Fire up Terminal and type:
defaults write com.apple.iTunes full-window -boolean YES
to move the buttons back to the top. If you want to move them back to the side, replace YES with NO.
I think the icon for iTunes 10 is ugly and hopefully isn’t starting a trend for OS X or is indicative of things to come from Apple.