The USB keyboard on early model G3s and iMacs stopped working after the 
USB code was cleaned up sometime between 1.4.2 and 1.5.  There is an open 
PR on this problem (12894) and I have discovered some additional behavour 
that may help isolate the source of the bug.

Testing with -current (as of 5/25/2001) on a G3 with both ADB and USB 
capability I have observed:

With both ADB and USB keyboards installed the ADB is dead during boot but 
the USB is responsive, however both are dead after the system has booted 
to the login prompt.

With only the ADB keyboard installed the ADB works during boot but is 
dead after the system gets to the login prompt.  The USB keyboard is 
usable if it is plugged in _AFTER_ the system gets to the login prompt.

With only the USB keyboard installed the USB works during boot but is 
dead after the system gets to the login prompt.  The ADB is also unusable 
if it is plugged in at this time.  Unplugging the USB and plugging it 
back in produces the expected USB events which are logged on the console, 
but the keyboard is still unusable.

It appears there is some undesired interaction between the ADB and USB 
keyboard designation in the system.  Possibly some flag variable is 
reversed?

Hope this helps someone with a better understanding of the code.  As 
always I'm happy to test patches if anyone has an idea.

-bob