Well, when my time comes to purchasing wheels, I'll be going with 18's. Brion (Fyxtion) in Milwaukee has 18" wheels. Mark V here in Chicago has 18" wheels.
And as for the strength issue. I have heard they are very strong, but they can bend if you abuse them enough.
Phil (dwx) has a set (in 17"), and he hasn't bent his as far as I know. And he's about as hard on wheels as anyone except Jon (Ralyrcr).
Hope this helps.