the file size has nothing to do with it according to apple advisor I spoke to at support. We has concluded that the iOS4 limits video clips that can emailed to 54 seconds long. No matter the size of the file. take a 720p video and and export your imovie at the highest quality then try to email it. Mail will trim the clip to 54 seconds every time regardless of file size or length. As long as your video is 54 seconds or shorter, mail will not ask you to cut the video down to be emailed or sent to mobile me. the guy I spoke to at apple support has sent a letter to apple engineers about this issue and is going to call me back in a few days about it so I will post whatever answers I get. I emailed myself a video done with imovie app and it was 107mb but was exactly 53 seconds long, and it went through without asking me to cut it. I went back and changed one transition to 2 seconds longer making the video 55 seconds and it had to be cut. After cutting the video and emailing it to myself it showed up as 54 seconds long and 105 MB.