Screws seem to be the first thing to go for me. I get rust in the allen cup (is that even the word) and I worry I'll round it out trying to remove the thing. Stainless parts shouldn't do that, but I always find a few that don't turn out to be stainless.
I once had a lock seize up on me after being wet for a few hours. It was a Specialized. I took it back to the store and they replaced it with a better one at no cost.