nVidia has posted a paper about shadow volumes. Here is an abstract:
"Combining efforts from Brown University and NVIDIA Corporation, this paper presents a set of algorithms for rendering shadows using the stencil buffer and the shadow volume technique. Using a series of techniques for culling, clipping, and simplifying shadow volume geometry, it is possible to achieve greater performance than previous methods. The algorithm builds on previously published algorithms by Crow, Everitt and Kilgard, and Lengyel.
The paper can be found here. It also includes a demo.