Apple added to iMovie '11 an ability that allow you to export 1080P video to YouTube.
"iMovie '11 lets you publish your movies in more ways to more places. You can export movies to iTunes and watch them on your iPhone, iPad, iPod, or Apple TV. Share them with your friends on Facebook. Premiere them with a YouTube or Vimeo audience. Publish newsworthy content to CNN iReport. And you can create a video podcast in iMovie and send it directly to Apple Podcast Producer. When you export HD video at full 1920-by-1080p resolution, (emphasis added) whatever you share will stun everyone," reads Apple's iMove '11 page.