There's been a lot of progress on Mesa geometry shaders in the past few weeks. The latest word to report on this OpenGL 3.2 feature is Nouveau's NV50 driver.
The Nouveau NV50 driver is what supports the NVIDIA GeForce 8 series graphics cards through the GeForce 300 series. This geometry shaders work was done by Bryan Cain, who previously worked on Gallium3D "GS" support. Already there has been NVC0 patches for geometry shaders with the newer GeForce 400/500 "Fermi" series.
The NV50 geometry shader patches can be found on the Mesa mailing list.