Michael McCracken says:
I just had a serious urge to tag my emails. And chats. And, of course, songs.
This is something I would LOVE to see in Mail. I'd pay for it!!! I have so many emails floating around and so many areas to deal with that being able to assign an arbitrary tag (keyword is probably a better name, and less buzz-wordy) would be a huge benefit to me.
A commenter pointed out there is a plugin for Mail called Mail Tags that aims to do this. I'm going to try using this, but it would be great to see this built into Mail itself in the future.
Apple, are you listening?
UPDATE: It would help if I linked to the damn thing…
Apple, are you listening?
I doubt it, the Mac OS X application division has lost the plot. It might be an idea for you to write one though.