>> Since I don't think it migrated got over here (yet): The Destiel reference is a popular meme on Tumblr.<<

It's not common, but I've seen a few examples.

>> The main fandom ship kind of went canon, with Castiel saying, "I love you," to Dean, and Dean... not really saying much of anything back? <<

Well what did you expect? Dean's level of emotional constipation is equivalent to a sloth climbing down to the ground once a week to shit and worrying the whole time about getting eaten by jaguars.