Ask HN: Malicious USB devices

Hack-a-day has had two interesting posts this week concerning publicly available USB devices.

http://hackaday.com/2010/10/29/tiny-usb-business-card/

http://hackaday.com/2010/10/30/this-is-a-peer-to-peer-filesharing-network/

Comments were riddled with "Beware of malicious USB devices".

This got me thinking. There could be a lot of cool applications of public USB devices if there wasn't such a security issue. USB is great because it's so cheap to implement. What alternatives can you think of? What interesting applications can you think of?