PiFace appeared on TV news. It’s behind the latest workshop to allow children to connect a Raspberry Pi up to monitor a cupboard. It’s a fun example that shows what’s possible.
http://www.itv.com/news/granada/update/2013-01-08/computer-tells-world-when-y…
A reed switch is connected to the PiFace and a magnet is stuck on a cupboard door. When the door is opened the circuit is broken and PiFace causes the Raspberry Pi to tweet and issue a verbal warning. The whole project only took about 20 minutes to make and reusing a previous workshop that used an animatronic chicken to follow and read out on twitter.
The first in a series of tutorials ‘Easy as Pi’ describes how you can make your own.
PiFace 
Bought a Pi-face yesterday – it arrives this morning. Where online can I find documentation/project suggestions/test software?