I tuned my 09 JK 2dr 6spd with Superchips. I experienced a very noticeable improvement in accelerator pedal response. The SC software modifies the electronic throttle circuit, giving greater throttle opening under the hood for a given amount of tip-in pedal input. It's a nice, brisk improvement for driving around town.
The power curve increase on any of the SC tunes is harder to discern, but the engine does rev more freely and has a seat-of-the-pants power increase above 3,500 rpm. Not huge, but it's there. I use the 89 tune with 89 octane fuel. I can easily get away with 87 octane around town, but I have occasionally noticed some light "flutter ping" when agressively going up through the gears. My gas mileage did not change in either direction - basically always 15.0-15.5 mpg around town.
You notice the impact of the SC tune most when you go back to the stock tune to visit the dealership. You find that you can't wait to get back home to reload the SC tune of choice.
Also, there are NO long-term damages to your engine, unless of course that a SuperChip tune gives you the urge to drive like an idiot.... and you aren't aware of what engine pinging sounds like.
FWIW: I would get another SC Tuner with out hesitation. I also try to use the recommended grade of fuel, or just take it easier until gas prices drop a bit.