UPDATE (19-Sep-2012): as promised, I've thoroughly tested the brand new TV output support.
1.) with wired connections (that is, via the VGA or the HDMI connector – I didn't test the RGB / composite ones), TV out works with the following types of videos:
a.) ones that aren't supported by the iDevice's hardware decoder (they aren't H.264 videos) and, therefore, can be played only via software decoding,
b.) ones that are supported by the HW decoder AND they're ALSO in one of the iOS-friendly formats (MOV / MP4 / M4V)