Juliet is still there in "Goodbye, Columbia." Clearly whatever she's up to hasn't been ascertained yet.
"Goodbye, Columbia" airs October 11, 2010. Here's a cute picture of Blair from the episode.
Serena at Columbia. This is going to be good.

Gossip Girl Season 4 Episode 5 Quotes

Serena: B, can I talk to you for a minute?
Blair: Yes. [to Minion #1] Five paces behind. For privacy. [to Minion #2] Ten for you.

Researching women of power so I can better forge my path to become one ... Sarah Louise Palin!? [to follower] Do you even want to be a minion?!