Just so some people know....
Not everyone has problems with Leopard. They're quite magnified here because people come to forums to get help for their troubles. I'm running Leopard on two Macs and neither of them have had any issue. The only problem I ran into (with X11) was fixed with 10.5.2. Hell, if anything, Leopard seems to run faster than Tiger (after having used Tiger on this same machine for almost a year), and doesn't appear to use much more resources. A little bit more RAM, but RAM's cheap these days, and not enough more to be an issue. Since the 10.5.2, my CPU seems to run cooler, even.
Not everyone has problems with Leopard. They're quite magnified here because people come to forums to get help for their troubles. I'm running Leopard on two Macs and neither of them have had any issue. The only problem I ran into (with X11) was fixed with 10.5.2. Hell, if anything, Leopard seems to run faster than Tiger (after having used Tiger on this same machine for almost a year), and doesn't appear to use much more resources. A little bit more RAM, but RAM's cheap these days, and not enough more to be an issue. Since the 10.5.2, my CPU seems to run cooler, even.