When Serena and Blair were discussing how Steven wanted to get back together with her after he left the Thanksgiving celebration, Blair tells Serena she must be in seventh heaven. This is reference to Barry Watson's (who plays Steven) lead role on the long running family drama series, 7th Heaven (1996).
Chuck mentions to Nate the idea of building a hot tub time machine. Sebastian Stan (Carter Baizen, who doesn't appear in this episode), has worked on the movie, Hot Tub Time Machine (2010), playing the character of Blaine.