Yes, the new 11 spd Shimano are only theoretically the same ratio as old campy (1.4:1) but in my setup it shifts great and setup was dead easy. I bolted it on, tightened the cable in the highest gear and it was pretty much good to go with a just a tweak of the adjuster - I didn't touch the B-tension at all. And my frame is a beat up old Fuji that has had the rear spacing spread from 126 to 130mm and with a hanger that is not dead straight. But my caveat is I've not ridden many modern bikes (none actually) so I can't really compare the shift quality to a well setup new bike.
So if someone else wants to try it I see Bikewagon are selling Shimano 105 5700 rear derailleurs for $25 right now....