It does raise some interesting issues,
Me and my friends all carry pen drives like others carry mobile phones and we regulary swap files from each others pcs,
Such as mods, save games and so on.....
I never really scan my friends pen drives when they chuck em in my usb port but i always thought that if there was something nasty on them that my antivirus would start going mental,
I may have to rethink my secuirity on my pc.