99.99% of the problems people are posting are probably machine specific. It's not Leopard that is causing the problems, it's probably because they didn't install the OS correctly, have system hacks, or have certain hardware specific problems that relate to Leopard (iMac freezes for example). I find it almost amusing that when someone has a problem, they automatically blame Leopard. When I have a problem (which I rarely do), I first check to see if others are having the same issue or if perhaps I might be doing something wrong. It's not an issue for Apple unless it happens to a statistically significant amount of users, is repeatable, and disrupts the function of your machine. Just because YOU can't play "insert your favorite game title" doesn't mean that Leopard is crap.
And just because YOU don't like Stacks doesn't mean Leopard sucks. For everyone who hates stacks... there are a dozen people who like that particular feature. Get used to it. I read one post where some guy said that he wouldn't upgrade to Leopard unless the "fixed" the transparent menu. For him, the WHOLE OS was broken due to this minor inconvenience. WTF??
I've installed Leopard (ran a simple upgrade from Tiger) and I'm having none of these problems. Or if I do run into a "problem" it is so insignificant that I don't give it a second thought. For example, repairing permissions takes a couple of minutes, but since I rarely do that, I could care less. As for the transparent menu? I found a word around that took me all of 5 minutes to implement! Instead of people struggling to make Leopard work for them, they should spend more time learning how to use it and adapt to some of the newer features. People go to great lengths to fight progress. And yes, Leopard is progress.