I can't say if it's USB or not causing my problems or the fact that MS's
F-Lock keyboards default to it being off, but with my USB F-Lock keyboard, I
cannot hit F8 to launch Safe Mode. So at the very least, keep a regular PS/2
one around in case of disaster (like in my case, where I cannot gain any
kind of admin access to my machine...I'm even blocked from reinstalling the
OS!)
For performance and getting away from legacy, I'd recommend USB, though. My
issue is probably more related to how Windows boots than a flaw in USB
itself (my keyboard is enabled at POST, disabled during initial Windows
init, and then re-enabled during startup.