We recently upgraded from an aluminum Santana Sovereign to an Arizona cf tandem. Lots of changes besides the frame (regular wheel to Rolf wheels, alloy fork to cf, Shimano 8-speed to Campagnolo 10-speed, etc), but we are really happy with the change. The new bike is *much* lighter, which is really noticible going up hill. But the biggest change is stoker comfort. My wife would not consider riding the Santana without a shock-post, but she is perfectly happy with an regular post on the Arizona. We really could not be much happier.
Scott Harper