I just compiled up vanilla-sources 2.6.15, and noticed that the kernel developers changed the Event Input code so that it requires the latest UDev to properly work. This was a kicker when I tried to get the X11 Synaptics touchpad driver working and it wasn't finding the device in /dev/input, like it had in 2.6.14 and below. I've already unmasked sys-fs/udev to pull the latest in, and can confirm that updating UDev corrects this problem.
*** This bug has been marked as a duplicate of 117680 ***