I have an '03 H2 that had a whipple supercharger installed in '03. When I purchased the vehicle over a year ago, the whipple's pulley was worn down and was making the supercharger's gears clanking around. The oil was ok and after taking the supercharger apart the gears looked fine...but I only had two options...
1) Try to find a shop to recondition the supercharger.. (since whipple had long since changed the design and no longer "repaired" the pulley)
2) Buy just the new version of the whipple supercharger (the mounts and such didn't change since '03)
So I went with number 2.
The other issue with the supercharger is that it is extremely hard on the drive train with the added horsepower.
When I got my Hummer it only had 33k in miles, and the transmission looked like it had been recently replaced just before I got it.. I would bet under warranty.
So if you want the added HP, just be prepared for stuff to break.
I really can't speak for how a non-charged H2 drives, but with the supercharger, it feels right. I can steep on it and get moving really quickly (instant mpg reads 0). No problem when towing and getting up to hwy speeds.