To make it worthwhile to me, all you need to do is work it into tag discovery. Say I go to the page of all things that are titled #writing. It asks me if I want to follow #writing. It might also suggest #writebetterdammit, #writingsucks and www.readwriteweb.com. If I can click "similar" next to #writebetterdammit, then you have metadata suggesting that at least one user thinks #writebetterdammit is similar to #writing but #writingsucks and www.readwriteweb.com are not. If I also have a radio button that says "follow and group" next to all, that's another piece of metadata for you. Finally, on my page let me rename my "groups" so that "#writing#writebetterdammit" becomes "Writing" (or "kleinbl00's magical writing group"). That's more metadata for you.

The trick is to make that grouping pleasant and fun. I'd go as far as to say handing out badges for every (20? 40? 100?) grouped tag would be altruistic; after all, those badges don't do you any good, they're the gift that keeps on giving.

Spitballing.