I had seen this information a while back about what is the best video format to upload to get the best quality playback from YouTube videos. Well, obviously there is a (corny) video to go along with the information. Boy, that DivX sure gets around.
Just to sum up, save your video with the following attributes:
* MPEG4 (Divx, Xvid) format
320×240 640×480 resolution (*updated recommendation)
* MP3 audio
* 30 frames per second