I haven't rebooted in about two weeks. And that's hardly a record. Ever since 10.1, I've found OS X's stability to be VERY good (10.0 was garbage). There will always be third-party apps that are buggy, of course (as with any platform), but they never bring down the whole system. At least not in my experience.
Please remember that this is a support section of the site.
As such you're only going to hear the negative side of user's experiences (why else would they post?).
How many people would have been put off buying an iPod if they'd read the apple support pages for the iPod first (full of people with faulty iPods), i'm betting lots.
Unfortunately, when something which is absolutely standardised becomes widespread (ie the iPod or Mac OS X - which only runs on a hundred or so computer variations after all) even the smallest failure rate becomes big news - search google for "iPod Nano screen". Guess what - the top link isn't positive!
OS X is an absolute rock (for me anyway). My macs get shut down only when software update says they have to be - my PowerBook has basically been on since I bought it (barring tonights new version of Quicktime that necessitated a restart) 3 weeks ago.
My beige box has been up and running since sometime in Feb of 02 (or maybe 03...been so long I can't remember <G>) on 10.1.5 as a file server...so yea, it's pretty darn stable.
The laptop usually stays up for a few weeks before I restart...just depends on if there are any updates supplied from Apple which require a restart or the occasional accidental power downs (I don't know how I manage to do it, but I do). It's main use is as my main machine and for web & graphics design...so I don't baby it.