That is very curious - I had been hanging out in the Apple TiBook Forums covering the issue of noisy fans about a year or more ago and everyone spoke of two fans - the "quiet" one on the right side under the keyboard that cools the GPU and the blow-drier that lives in the rear center.

Nobody ever responded to my queries asking if anyone could actually feel air coming out of the vents.

Ah-hah I see the link you sent is for the 667 & 800 TiBook DVI, not the older 500 & 667 TiBook VGA ("Onyx" I see they were referred to as) model. I will nose about the site, though.