I'm a typical early adopter but my trust in apple has paid off. 10.5 Works Flawlessly on my old 17" CD iMac, My new 2.66 Mac Pro, My C2D MacBook My mums 20" C2D iMac and even my old Dual 450 G4. All of them were (erase & install) Clean installs except my mums iMac. My mums Boyfreind did manage to delete a load of work when he put it in a stack and then deleted the folder and emptied the trash. I did laugh!