So I just flew to Denmark for the summer, leaving my moped with a friend back in Cambridge. It had been parked outside in front of one of the MIT dorms for a week, I handed over the key on Sunday night, and when he went to move it Monday afternoon it was gone. He found the cut lock (it was a Kryptonite hardened chain, so someone knew what they were doing).
It's a 1978 Motobecane 50V. Black, mag wheels, sissy bar, turn signals, mirrors, last seen with bright orange saddle bags. Pretty distinctive with the add-ons, but they could be removed. The kickstand red, and unless the thief is really smart, that will probablly be its most distinguishing mark.
Like I said, I'm in Denmark until August, so I can't keep an eye out for this. If you see it, contact me and John Williams - johnw AT mit.edu. John's the guy I lent it to, and this theft wasn't his fault (I parked and locked the bike...), so don't give him a hard time or anything.