I've discovered an extremely irritating bug in OS X. If you're using the trackpad when copying a file from the filelist in Finder to the sidebar, if your finger accidentally slips off the pad, the file disappears! It doesn't go to the sidebar, and it doesn't remain where it was originally. Great undocumented feature of OS X. Anyway, since the file I was trying to copy was addressbook.app, I can't run the addressbook anymore. I've read where the only way to reinstall the addressbook is to reinstall OS X entirely including all the updates that have been installed previously. Does anyone know of a way that I can just reinstall that one application instead of having to go through the reinstallation of the entire OS? I'd be extremely grateful for any advice.