I have been riding some clincher race wheels (Hed Alps front, Zipp 404 Clyde rear w/Powertap) quite a bit in training. I actually have some junk (read: tougher and more flat-resistant) tires on them right now and have a set of Conti race tires waiting for the next time trial. I raced on them yesterday in a triathlon in Clermont, where the roads are hilly and badly paved, and left the tough tires on. I'd rather not flat than worry about 10 seconds lost to rolling resistance.
Edit: they've held up just fine and I figure I might as well get some use out of 'em; I don't race every weekend like some.