I have been around Macs enough to see them crash in a variety of ways. My favorite is when the busy icon spins forever while freezing everything else. It is technically not a crash, but it's sometimes more frustrating than a crash. I haven't seen much of it in 10.3, but it was all over 10.1.
I have never upgraded past 10.1.5. I leave it up w/o rebooting for 30+ days. I've never had it crash. Have had a couple of apps go wonky, but just kill em and problem over.