The official Apple document states for 10.2.6:
Improves compatibility for MacSoft Unreal Tournament 2003 on computers with GeForce 2MX and GeForce4MX graphic accelerator chipsets.
I have a 12" PowerBook with a Geforce4 Go 420, which is an whatever crippled Geforce2 or 4. The 10.2.6 must somehow tweak the graphics driver for the Geforce, because it not only affects UT2003, but my screen saver, too. I run SereneScreen's Marine Aquarium which is relatively demanding. You can run it showing the FPS on the bottom of the screen. Before 10.2.6 it was around 75fps, now it's up 95fps. Nice side effect.
Have others seen any increase in graphics performance in other apps?