the only cons to a supercharger are the cost and potential imprisonment. gas mileage is the same under normal driving, but is a bit worse under spirited driving (the extra power obviously doesn't just come out of thin air).
there are a lot more pros though. I have the ESS 575 kit, and I can confidently say that I don't crave any more power. it's scary fast. unless you fit 305s or bigger in the rear, you won't have enough grip to put that kind of firepower down at any legal speed. I can't recommend the supercharger enough - you have to experience it to understand what everyone is talking about.
if you have it in your budget, there's no excuse not to get it. just do your research before deciding which kit is right for you. plenty of info available on this forum. below are a couple more detailed reviews I posted. good luck.
http://www.m3post.com/forums/showthread.php?t=496580
http://www.m3post.com/forums/showthread.php?t=551151