UPDATE (September 2012): After last iTunes update this feature makes dock crashing. See this thread.
Via this post i found a gorgeous trick. I always wanted a pop-up notification displaying the current song title (when changing track, for just a few seconds). I used a Growl plug-in in Snow Leopard, but now it’s possible to enable a similar feature in Lion just with a comman line trick via the Terminal.
defaults write com.apple.dock itunes-notifications -bool TRUE;killall Dock
Then start iTunes and try playing a track. Neat, eh? The pop-up fades away after a few seconds. To add the iTunes icon to the pop-up window, type the following into a Terminal window:
defaults write com.apple.dock notification-always-show-image -bool TRUE;killall Dock
To deactivate the pop-up at a later date, quit iTunes again, then open a Terminal window and type the following two lines:
defaults delete com.apple.dock itunes-notifications
defaults delete com.apple.dock notification-always-show-image;killall Dock