iChat, Snow Leopard, and broken audio workaround
If you’re having audio issues with iChat on Snow Leopard (no audio, only one person gets audio, etc.)—particularly if you have a Time Capsule and a MobileMe account—here’s an unfortunate workaround:
Try turning off Back to My Mac.
I turned it off in System Prefs on both Macs in question, and also turned off Enable NAT Port Mapping Protocol on the Time Capsule and audio during chats and screen sharing works again.
Hopefully Apple has a fix for it (and for the damn annoying status message bug with AIM accounts) soon.
