dc42:
It may be worth putting a current limiting resistors in series with your 5V and ground ICSP pins then.
That's a good idea. I'll put that on the next version of the board I'm making. Also, I'm starting to like TVS-es -- you can get 6 of them in a small 8-SOIC; if I can find the space for one per exposed header/connector, I think that'll be good.