I am using CS(1) on Leopard and it definitely has some quirks—for instance, the only way to open files is to do so from within Photoshop- if you double click a PSD (or any other photoshop-assigned file format) it will launch Photoshop, but the file will not open. Dragging and dropping to the photoshop icon doesn’t work either. You have to actaully use the “Open File” dialog every time. There also seems to be a bug where clicking the Marquee tool in the Tool Palette nearly always opens a submenu, instead of just selecting the tool. That may just be me clicing the wrong part of the icon perhaps…
In any case, the file-opening bug is definitely annoying, but not a show-stopper—I have an older G4 1.25ghz powerbook, so it probably doesn’t make sense to upgrade to CS3 given that. It’s too bad Adobe doesn’t appear to offer any patches for the problem(s) I listed, but again, no show-stoppers. Good luck!
Oh and if anybody does know of a patch for these issues that I just didn’t see, please post a link… Thanks!