Just got done emptying half my desk o' junk and haven't found it yet. However when I was looking through the documentation of two of the engines we are evaluating for use at work I decided to poke at the shaders section...

Right now both are recomending using a seperate pass per light using a 2.0 with a 1.4 fall back shader for optimum results on DX9 hardware for per-pixel lighting. Seems as though that might be something to investigate for 3DGS as well.

Ugh - back to the stacks...
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Did some more looking today - I must have my notes at work right now. However there are a couple articles that quickly glaze over the issue on Gamasutra and GameDev.net. Also when looking online use the keywords "depth test."

As far as chip specific techniques I have been implementing an optimized path for ATI chips the past few days. It uses the HyperZ technology which is ATI only. The premise is similiar, but the ATI cards can process larger chunks at a time than other manufacturers and writing a pipeline for that specific chipset comes in quite handy.

For anyone who is doing a lot of shader programming consider working in fragments as opposed to complete shaders. NVidia and Microsoft both have handy fragment tools which will allow you to assemble predefined shader fragments into complete shaders which aids in the process of developing multiple paths (you will still need to implement switches in C-script...but that is pretty simple).