In a scene where the stunt doubles are rehearsing a fight, they are Jared and Jensen's actual stunt doubles.
Jared Padalecki (Sam) and Jensen Ackles (Dean) have both said that they were skeptical at first about 'playing themselves'. Jensen, speaking about it, said that as long as he was never asked to break character as Dean then it really didn't matter what they were called or what situation they were in. Both actors have said that this episode ranks high on their list of favorite episodes.
The tweets "Misha" tweeted were real. He actually pulled out his phone and typed them as the camera was rolling.
In the alternate universe, "Jared" and "Jensen" don't talk to each other. In real life, Jared Padalecki and Jensen Ackles are best friends and were each other's groomsmen.
In "Jensen"'s trailer, Sam and Dean see a clip from his work in a soap opera. The clip is an actual one from Jensen Ackles's work in Days of Our Lives (1965).