Apple's latest preview of OS X 10.5 had a little bonus over the usual glitch fix. Inside iChat was a new preference pane, called Answering, a feature that lets you record a video away message with your iSight.
Also Macrumors.com is claiming that this will be linked to the rumored iPhone Call Ahead feature. Interesting.
Leopard iChat Answering Machine [MacRumors]