This post on the Shugashack gives a reply from Valve's Gabe Newell to a question a bunch of folks have been asking since the developers participating in the PowerPlay project (story) have been announced, why there's no mention of participation by id Software. Here's Gabe's answer to that question:

Yahn's been talking with John quite a bit about this. John told Yahn he wants to take a stab at rewriting the Linux IP stack and a soft modem driver to see how much latency he can remove, and use that to pressure Microsoft into cleaning up the Windows stack. That would be really useful data to have.

Our list of things and John's list of things are pretty much identical, but John passed this time around on being part of the public announcement. Yahn's take was that John was just tired of answering questions from the press...<snip>

Certainly with everything John has done already (e.g. OpenGL) he's paid his dues into the next century, so if thinks it's other peoples' turn to carry the flag for a bit, that's totally justified.