I was working on the Paynetech Beatsbyteensy (www.paynetech.c...) and i killed it in a fairly unique way.
I don't know if this is due to the PS/2 library being imperfect, or the minipac being overly sensitive, but a small proportion of the minipac crashed completely, despite being entirely on a single chip.
I don't know if it was the arduino PS/2 library being imperfect, the interrupt timers being poorly timed (due to audio load) , or simply the minipac being overly sensitive. a Reset fixed it of course, but interesting nevertheless.
A minipac is a 32 way button input interface which masquerades as a PS/2 keyboard, typically used for arcade cabinets.