The State of the Art
A lot of the projects I've discussed here are just starting to become stable. The open source nVidia and ATi driver development efforts are focusing now on using Gallium, and it looks set to become the core driver model for open source operating systems.
In 2009, Gallium has gained a state tracker for X.org, which means that any of the supported extensions can be accelerated without X needing any device-specific code. It can also be used for accelerating OpenVG applications for fast 2D vector graphics; although there is little point offloading simple line drawing, things like antialiased Bezier paths are still faster on the GPU.
Simpler drivers and support for more userspace APIs means that the future is bright for open source graphics acceleration.