If you have an account on YouTube for an organization or business, and are using iMovie 10 to create videos for it, you’ll likely run into two pieces of bad software design.
First, you should know that iMovie doesn’t have a Save or Save As button, because it saves your work as you go. To produce your movies, you use the Share button or the File/Share command. That’s not a problem.
If you want to share a movie on YouTube for your own, personal account, this works great: just choose YouTube from the sharing menu, enter your Google ID and password (Google has combined regular accounts with YouTube accounts), type a name and description for your video, and you’re done.
But this method will not share your movie into your organization’s account, even if you’re the account owner. You have to create a file on your hard drive instead (choose File from the Share button or Share menu 
), log into YouTube as your organization or company, then manually upload the file. But this creates another problem: when iMovie shares to a file, it doesn’t encode it for Internet Streaming, so YouTube has to do the processing on its end, and your movie will take longer to be available. And YouTube will warn you about this. Older versions of iMovie had a checkbox for “Fast Start”, but that option doesn’t exist anymore.
If you’re thinking of opening the movie in QuickTime and re-exporting with Internet streaming enabled, think again if you’ve upgraded to QuickTime 10. For some reason, Apple removed the option there, also.
Until Apple gets these issues fixed (or will they? Are these bugs or features?) I’m going to stick with Adobe Premiere Pro for creating YouTube videos.