I think I first saw it running on a Geforce with 64MB of RAM. Even then it was smooth as butter.

Now that I think about it, Mac OSX was doing GPU compositing back in 2000/2001 and those machine usually only had about 16MB of VRAM. I remember it running fairly well on a 2005 MacMini G4 with 32MB of VRAM.

The first versions of Mac OS X only supported software rendering. GPU compositing didn't show up until 2003, in Mac OS X 10.2. It was branded as "Quartz Extreme".

I did not know that! There was about a 6-7 year gap between 1997-2004 where I didn't really do much with Mac's. But your timeline seems spot on, it was 10.3 when they introduced Expose into the system. A great demonstration of the GPU functionality in action.

Actually, IIRC the only requirement for DWM to work was a GPU that supports shaders, because that's what makes the window border translucency/blur effect possible.

Compatible driver, actually. There were at least DWM 1.0 (Vista) and DWM 1.2 (Win7), but Intel never provided a compatible driver for... 915? Series, so you could't enable composition on them, despite hardware were capable enough.