When you use a shared PC, sometimes you get to share other people’s passwords. Especially when people are kind of led to believe they’re safe.
I was wandering around the security landscape last week and was at a client’s business which is quite large and has kiosk PCs for employees and visitors to use to access the open Internet (they lock social networking and other stuff down pretty tight on the business network, so usually you see lines of people tapping away at the rows of kiosk PCs).