in referencing a specific article on Google Groups today, I got irritated by the URL including the message ID wrapping. So I registered and built msgid.net (it'll go live tomorrow). It shaves at least 20 characters off the average message ID URL. I'm quite chuffed with it.
The dev URL is available if you want to play with it today. [2001-08-29: it's live now - no need for dev URL anymore]