Yesterday the Apple TV got an over-the-air update that broke the awesome PlexConnect app that brought Plex to unjailbroken Apple TVs. If you've already updated, there's a way to fix it.
The Apple TV update was actually pretty solid, bringing apps for Vevo, the Weather Channel, Disney, and the Smithsonian Channel. Unfortunately, it broke the PlexConnect hack that let you install Plex using Apple's Trailers app. Fixing it takes a bit of work (and you'll need to be familiar with the Terminal), but it isn't anything too hard—all you need is a microUSB cable and a Mac with Apple Configurator installed. Check out the link below for the full instructions.
AppleTV + SSL + PlexConnect | Langui.sh via Mac|Life