Definitely is. The obvious thing is that they've been moving the UI processing to the GPU more with each generation. By Leopard the CPU won't have much at all to do with the UI. But they have done a lot of tightening and tweaking in the kernel to speed things up too.
As far as adding things, that impresses me too. They advertise this massive Core Animation to make things fly around, warp and morph all over the place -- but they're nice enough to make sure that will all happen on the GPU instead of slowing down your system.
I know people running four+ year-old G4s who say it's faster running Tiger than Jaguar. Show me that with Vista.
I’m one of those G4 folks. Have one small client with a network of 4 G4s with a G5 (PPC) server. Got the G4s used for less that $500 each. I just keep upgrading the OS and apps. Quite economical - plenty fast enough, stable, secure, extremely low maintenance.
Eventually the whole thing will have to move to MacTel. Even faster I hear, but I hate the bleeding edge. Hopefully by then, there’s no glitches and, heck, maybe I can get’em some used intel boxes.
What might be most interesting is what happens in the high-end PC market when the whole idea of “buy a Mac and run Windows or OS X - or both” filters through. IMHO, and others, that could be the biggest desktop industry shakeup in decades....