I tried one at PAX, it was okay...? The existing 360 pad is pretty much perfection so it doesn't feel any better, just different. I don't think the bumpers feel as good.
Oddly enough we got a bunch of donated controllers from MAD CATZ and the MLG Pro controllers are actually pretty incredible. You can swap in a PS3-style dpad, and sliding the analog pad around its extremities feels perfectly smooth (as opposed to the gritty feel of the 360 pad/dual shock). It really is the damnedest thing. I always thought third party pads were ass, but this one is super good. Then again, I think they retail for a hundred bucks or something.