I swear I've seen one of these towbarless tugs in SFO
many years ago bring a UAL 742 to our gate from MX
to the hanger.. whether they stilll have them there I don't know. Looked really neat when they dropped/rolled off/disconnected (whatever it was =P), you could see the whole front of the plane compress back down onto the oleo almost like on landing.
Edit: Aloha at HNL does something similar to spinouts at their jetways behind gate 34 at the Aloha/Hawaiian concourse. They just pull them out just enough just to make the tight turn as there is limited space on the taxiway at their east gates. On my trip home from Boston 2 trips ago, we broke a towbar on pushback. Taxied back on our own power to the gate and had to inspect the nosegear. Everything turned out okay and I am home safely
[Edited 2004-08-20 12:34:42]