In Blair's dream, she is inside the movie All About Eve (1950). She has previously only dreamt about Audrey Hepburn movies.
The purple dress that Serena wears was also worn by Shantel VanSanten as Quinn James on One Tree Hill (2003) in season 7 episode 5, Your Cheatin' Heart (2009).
Leighton Meester's (Blair Waldorf) real life brother, Alexander Meester (Lex Meester) makes several appearances in the background of this episode. He can be seen as the person Blair is speaking to at the party (26:58) and then again, standing behind Chuck, after everyone hears what Blair said to Vanessa (31:33 and 32:10).
Nate talks about his rival J.P. Buckley looking like a younger version of J.R. Ewing Dallas (1978) , but that description is more suitable to describe Chuck Bass.