Pros Unleashes Intel Macs' power. Improvements over Tiger are great.
Cons Requirements are hefty, though my machines are supported. Performance should be better for PPC Macs.
Summary I'm completely satisfied with Leopard and I think it was a worthy upgrade to OS X. If Apple had made it more PPC friendly, things on my G4 would be smoother, but it runs great nevertheless. Don't hesitate to get this.