I took mine off. There's a distinctive rumble when revved, but not really a big difference at idle.
The thing to note as different is that I also put in its place a Raceland remote cutout to maximize the fun factor. Removal of the resonator & installation of the cutout was only $120. (I did the very simple electrical wiring.) It might be a little slower off the line when open, I'm not sure.
Floor it at highway speed from about 60 with it open and the butt dyno tells me that performance has improved, no question.
Here's a sample:
http://www.youtube.com/watch?v=bmCvTddcMmY
It gives the sound (closed) without the resonator and open (loud as hell). Not my car, but it sounds just like it.
Inherently, with a cutout, I'm leaking a little sound from the cutout device. So yours will almost certainly be quieter if all you do is put a pipe back in place of the resonator.