I just noticed this item on E-Bay:
http://cgi.ebay.com/ebaymotors/SNAP-ON-KWIK-LATHE-YA180-TO-TURN-ROTORS-ON-CAR-NR_W0QQitemZ140089074426QQihZ004QQcategoryZ63695QQrdZ1QQcmdZViewItem

item: 140089074426
Described as a "Snap-On Kwik-Lathe YA 180 lathe:
"This tool is for turning disc brake rotors without removing them from mostly import cars which I saw mentioned somewhere in the instructions. I have never used it but it seems to be in very good condition with all the threaded adjustments turning and moving easily. Included is a box of carbide replacement tips shown in closeup of the cutters on the machine. There is a selection of mounting bolts, bushings and nuts however I'm not sure whether they are enough for every import variation. The foam insert nesting the tool in the carrying case is pretty beat up by whoever put the machine in and out of its box. The working parts, like I said, are in great working condition. The manual is a Zerox copy and it's very light but readable. The machine itself weighs about 28 pounds but packed about 35lbs. What you see in the pictures is all you get but if I can answer questions please ask and I will try to answer."

Has anybody used these with Mercedes brakes? How are they? Is it still a current-model piece of machinery? I'm guessing that they use the drivetrain to turn the disc, so wouldn't work on Merc fronts, but maybe on the backs.