For the past couple of years, Funny or Die has had a celebrity "take over" their site for April Fool's Day. In 2010, it was Justin Bieber and then in 2011 it was Rebecca Black. There doesn't seem to be an equivalent young-ish, annoying celebrity this year for them to do that again. Jeremy Lin maybe?
Also, Adult Swim doesn't appear to be doing anything for April Fool's this year. I don't notice anything unusual about their Sunday night line-up, unless they're going to do something surprising at the last minute.