I was totally opposed to 18's before my girlfriend insisted (I mean sugested since it's not exactly a performance car anyway) that we put a set on my Accord, and I was pleasantly surprised. My Civic rides MUCH worse but I guess most of that may be from the stiff-sidewall Azenis tires. I've got PZeros on the Accord and it drives like a factory "sport sedan"; about the same level of harshness over bumps as a stock M3.

I don't hit potholes or curbs though. I'm sure they'd be egg shaped in a hurry if I did.