The K9 iso install went ok using a usb keyboard. I had other
problems though and did not get it properly installed, but the usb
keyboard worked.
It might have worked because the USB keyboard used the normal keyboard
interface so that it works early. Basiclly, it would be a pita to
write a USB driver just so that you can use your keyboard in the BIOS
and stuff that happens before the OS boots up.
I'm not familiar with USB keyboards, or USB devices, but I'm familair
with GNU/Hurd, and it doesn't support USB at all. :-) But it would be
nice if someone implemented such support!