Using iTunes 11.0.1, I tried to add some newly converted movies to my library for consumption on my Apple TV 2. This used to work well: ripping some movies from my DVDs, converting them using HandBrake with the AppleTV or AppleTV 2 setting and adding them to my media library. However, now nothing happens when I add the movie using Cmd-O in iTunes or via Drag-And-Drop from the Finder. Opening the movie via right click in the Finder in iTunes works however, and I can even stream to the AppleTV then. So what's wrong? I checked in the console logs, and can't find any iTunes related error messages.
Are you sure you're looking in the right Media section of your library? Try looking in Music Videos, TV, etc, in case iTunes is putting it in the "wrong" section.