At the BlackHat security conference researchers from Italy showed how to sniff passwords typed on PS/2 keyboard on the power outlet.

Poor wire shielding in PS/2 keyboards transmits the data also on the ground wire. Hackers can then read what you type on power outlets nearby.
The Italian researchers Andrea Barisani and Daniele Bianco also showed how to use laser beams to pick up the sound vibration from a users keyboard. Through some statistical analysis you apparently could figure out what was typed. Find out more details about their demonstration at BlackHat on InternetNews.

To be safe from these two attacks you need an all-in-one touchscreen device like the iPhone; Oh wait, the iPhone can be hijacked via SMS; just use pen and paper then.