Sometimes some applications do not quit like Indesign, Photoshop and iPhoto. I'm using Tiger. I end up using Forced Quit Applications (option-command-escape) wherein I see such apps are tagged as “not responding”. I think it's due to lack of memory. My PB only has 768MB. Does anyone experience this?
i think your RAM's enough... Have you tried the usual repair permissions and deletion of plist files for the problematic apps?