How do I disable Ping?
You can also restore the old arrow functionality



defaults write com.apple.iTunes show-store-link-arrows 1


I also suggest the following:

defaults write com.apple.iTunes invertStoreLinks 1



  This setting switches the default
  behaviour of the arrow links. By
  default (well, by default in iTunes
  10.0.0 and before) the arrows would send the user to the corresponding
  page in the iTunes Store, but you
  could also hold down Opt and click to
  be redirected to the corresponding
  list in your own library.
  
  Now, to reset it all to Apple's
  defaults... you can either do the same
  lines as above but replacing '1' with
  '0', or you can delete the settings by
  changing "write" to "delete" and
  removing the 1 from the end:


defaults delete com.apple.iTunes disablePingSidebar

defaults delete com.apple.iTunes hide-ping-dropdown

defaults delete com.apple.iTunes show-store-link-arrows

defaults delete com.apple.iTunes invertStoreLinks


restart when done.

I blogged about this when I read Tom Gidden's article