I see over at Doom3HQ that a certain Sebastian Sylvan emailed John Carmack with one of those high-tech questions he is so good at answering. Specifically he asked why stencil shadows were used over shadow buffers. Here's the response, which might mean more to you than to me:
Shadow buffers make good looking demos with controlled circumstances, but
when you start using them for a "real" application, you find that you need absolutely massive resolution to get acceptable results for omnidirectional lights, and a lot of the artifacts need to be tweaked on a per-light basis.
While it is possible to do shadow buffers on GF1/radeon class hardware,without percentage closer filtering they look wretched.
If we were targeting only the newest hardware, shadow buffers would have a better shot, but even then, they have more drawbacks than are commonly appreciated.