I came across this little gem this morning. The availabot is a small puppet llike gadget that connects to your pc via usb. It seems that you then assign it to one of your friends in your buddy list.They only support ichat on Mac at the moment but are looking to extend the application compatibility.
If the person is signed in the puppet stands up proud and tall. If they are not signed in it sits in a crumpled heap. The idea is a prototype being developed by Schulze and Webb ltd.

Schulze and Webb are a design shop in London and the availabot was shown at the RCA Show 2006.
Click here to see video of the availabot in action.