For every story like that there are hundreds and hundreds of people who upgraded with no problem and proceeded to complain endlessly about Stacks. With something as complex as a modern computer OS problems will happen from time to time. No operating system is perfect, not even one from Apple. As someone who regularly uses both Windows and OS X I vastly prefer the Mac. Sure it has problems, and it even really screws things up from time to time, but 99% of the time my biggest problem is that Quicksilver (one of the most useful free apps ever) unexpectedly quits often enough to be annoying, and that means less time trying to fix problems and more time doing what I want to do (which usually turns out to be nothing and I get bored. Maybe I should be hoping for more problems to give me something to do.)
EDIT: Yeah, what Mashiro said. He may not have very good taste in games, but he's right about this. In fact I'm taking his advice that he didn't follow himself, I'm waiting until 10.5.1 (coming real soon if Apple seeding a bug-free build to developers means what it usually does) or 10.5.2 before upgrading my MBP to Leopard.