How it works: Pretty much like anything else with a Record button -- you're on an audio or video iChat, you press that big red button, iChat thoughtfully notifies your participants that they're being recorded, and off you go. Audio gets saved as AAC and video as MPEG-4 (perfect for iPod/iPhone usage, perhaps a bit less perfect for sharing online) when you're done with the conversation. For presentation use, especially when combined with screen sharing and Quick Look, this instantly creates a no-frills alternative to recordable conferencing tools like Adobe Connect, GoToMeeting and WebEx -- at least for small meetings where everyone has a Mac.
Who will use it: iChat collaborators, podcasters, conference callers, and grandparents/grandchildren -- but only those with hearty hardware, as I'd expect iChat video recording to chew up quite a bit of horsepower. For those not quite ready to make the move to Leopard, ecamm's excellent and inexpensive Call Recorder 2 offers similar functionality.