These four defaults settings will disable Ping, hide the dropdown, restore the old arrows, and invert them such that clicking them will navigate the libary, not the Store. Boiled down from http://gidden.net/tom/2010/09/25/removing-ping
defaults write com.apple.iTunes disablePingSidebar 1
defaults write com.apple.iTunes hide-ping-dropdown 1
defaults write com.apple.iTunes show-store-link-arrows 1
defaults write com.apple.iTunes invertStoreLinks 1