There is a video on the YouTube highlighting comments John Carmack made during a Q&A session at QuakeCon 2009 where he was asked about hardware-based physics solutions such as PhysX, now owned by NVIDIA (thanks game\phys). The id Software technical director was already on record as being against dedicated physics processing units, but in his answer he elaborates. Here is our hand-crafted transcript:

Okay, hardware physics. I think I was fairly public about my thinking that that was a really bad idea, and in fact it was pretty clear to me from early on that the whole idea for that was to do a startup to be acquired.

I didn't feel it was actually... I actually had a really quite negative opinion about stuff like that because they went out, they evangelized, they got some people to buy a piece of hardware that I didn't think was actually a good technical direction for things on there; certainly was going to be supplanted by later generations of more integrated compute resources on there. I don't think it was a good idea, I certainly wasn't a backer of the company, and I hope NVIDIA didn't pay a whole lot of money for them.