Automatically delete temporary ~/Library/Application Support folders
I suggest you use a guest account on OS X if you want certain home directory files automatically erased for you. A guest account's home directory gets cleaned up when you log out.

From http://docs.info.apple.com/article.html?path=Mac/10.7/en/mh35549.html:


  Important: Files created by a guest user are deleted when the user logs out. A temporary home folder is created for the guest user’s files, but this folder and its contents are deleted when the user logs out.