iTunes 10.0.1 replaced the Genius sidebar with a Ping sidebar, and while you can’t currently restore the Genius sidebar you can disable the Ping sidebar.
Simply fire up Terminal.app and enter the following:
defaults write com.apple.iTunes disablePingSidebar 1
Want to take it a step further? Enter this two commands in Terminal to disable even more of Ping…
This disables the Ping buttons:
defaults write com.apple.iTunes hide-ping-dropdown 1
This restores the previous old-style arrow buttons:
defaults write com.apple.iTunes show-store-link-arrows 1
If you change your mind, just change the 1 to a 0 (again, all entered in Terminal).
defaults write com.apple.iTunes disablePingSidebar 0
defaults write com.apple.iTunes hide-ping-dropdown 0
defaults write com.apple.iTunes show-store-link-arrows 0
If the thought of using Terminal scares you, just download this AppleScript from Doug Adams.