After having installed the CAI and SCT3 tuner from Brenspeed several months ago, I have to say that I don't notice a whole lot of difference from stock, except at a dead stop, but 0-60 times don't feel any quicker. Feels no different.
Also, I've noticed absolutely no MPG increase, and lately, it's been going down even though I just cleaned the air filter. I noticed the drop before I cleaned it, and no change after. This could be due to **** gas though, I think they are watering it down and preparing us for even more ****thenal. Oh, I mean ethanol.

 

Your not going to "feel" a mod as small as a CAI and Tuner.
If you've ever taken your car to the Dyno or 1/4 mile than you'll see it there.

 

i definitely felt mine, on 89 octane, but no mpg increase

try taking the positive cable off the battery for 30 minutes or more and then reinstall the tune, sometimes the adaptive learning of these cars lessens the effect of the tune over time