I was able to borrow a Canon EOS 60D from my brother to test its 1080p video capture features. I shot this video in HD, but was unable to upload it to Youtube in HD using the version of iMovie that I own. The highest resolution is 360P.
I subsequently learned how to export an iMovie using QuickTime and was able to upload a HD version to youtube. This one should be viewable in high definition modes. The viewer can select the definition desired when watching the video. At the time I uploaded this video the highest resolution Youtube allowed was 480P. I am not sure why, as it should be 1080p.I think this is a problem with my version of iMove 7.1.4, as it only allows exports of 920x680, which youtube down samples to 480p. I may have to try a later version of iMovie, as we have a copy on my wife's laptop.