You never used 10.4, did you?
Certain versions of 10.4 would randomly corrupt the filesystem such that files would start occupying the same chunk of disk space (crosslinked files, I think the term is?)
I saw someone get fired because of that bug (well, not really. She was fired because she was working on client files on her computer and not on the servers, which were backed up...and then the files were hosed by MacOS.)
I think it wasn't until 10.6 or so that many of the mystery problems (that cropped up and went away if you deleted+re-added something...printer, network interface, so on etc) were by and large solved.
10.7 and 10.8 are by and large rock solid. Any time someone comes to us complaining their Mac is crashing randomly, it's *always* a hardware failure. 10.9 is quite solid as well; I wish I could say the same for my late-2013 retina MBP. That and the changes to how MBP's sleep (no sleep indicator, and no way to separate "screen goes to sleep" from "computer goes to sleep", without hacking plists) pisses me off, but has yet to piss me off enough to get down to the Apple Store to have it looked at.