Recording data and then building a video for YouTube could work. I'm guessing that's what Bungie was able to do with Halo 3 (recording the game, I mean). You can literally watch your whole session with a floating camera you can move anywhere at any time. Amazing feature.
Direct feeds to YouTube would be a nice novelty feature.
shouldnt take too much memory to do. For instance ghost lap files on GT5 are only a few kb in size. From a few i've seen, Games dont save the whole video, merely a set of data points that it later rebuilds the video from.
If games do this then it would just be a case of rebuilding the video to upload at a later point. Therfore not affecting the games performance