Apple Press release on Apple TV, iPhone and Youtube
(dated: June 20 2007):
To achieve higher video quality and longer battery life on mobile devices, YouTube has begun encoding their videos in the advanced H.264 format, and iPhone will be the first mobile device to use the H.264-encoded videos. Over 10,000 videos will be available on June 29, and YouTube will be adding more each week until their full catalog of videos is available in the H.264 format this fall.
Not sure what this implies, especially for uploading,but it's interesting in regards to the AVC/H.264 format.