Cons, engine life is slightly reduced (really depending on your maintainence habits), they cost an arm and a leg, they make it a bit tough to dial to peak performance, and vaccum leaks are a bitch to deal with...
Pros, damn they make the world of difference when it comes to power...
I would, however, rather spend 3,000.00 on other performance parts before I go blown. There are tons of odds and ends that will turn your engine from night into day. You could go pretty extreme on a normally aspirated engine for $3,000.00, but if you are at the end of your normally aspirated performance road then supercharger is the way to go.