I notice a big difference from when I buy all my speakers and a week or two later. My Infinity Kappa 5.25" component set sounds much different now than when it did a few months ago, the bass is a light more responsive and they overall sound much better. They take some time to break in. I did not do this with my subs though, didn't know much about car audio back then. They still sound good though. They're pioneer 12'*, they get really deep compared to other subs I've heard. I'm happy with the money I spent.
a good place to buy car audio online I've found is www.ikesound.com
, I buy all my stuff through them. I haven't had any problems with them yet, however, I do wonder how they get their prices so low.