The more I think about the delete issue, mentioned below, the more I think this is a bug and not a feature. I have filed a bug report in any case. Although, I do like that you can trash a file from within iTunes, I do not like that you cannot preserve a track's file. A dandy way for delete to work would be as follows:
1) delete a track from a playlist to just remove it from the playlist.
2) delete a track from its Master Playlist to remove it from iTunes entirely but preserve the file (I tried this hoping it would work, but it does not).
2) delete a track from library playlist 1 to remove it from iTunes entirely AND trash its file.
(I don't know why there isn't a remove command in iTunes, which would make more syntactic sense. The Finder's AppleScript delete command will send a file to the Trash.)
Needless to say, this bug affects several scripts which use delete to remove a track from iTunes without actually trashing the file. For instance, Make Bookmarkable will delete a track from iTunes and then re-add it. Under iTunes 7.6, the track's file is moved to the Trash; when it is re-added, unless the user has "Copy files to iTunes Music folder when adding to library" checked in Preferences, iTunes will presume the track's location is the Trash. Empty the Trash and bye-bye file. This is exactly what is happening to some users.
I can only hope that Apple will see this as a serious bug--it being part of the AppleScript component of iTunes, I am sorry to say that I think it is doubtful--and fix it soon.