Bill Murray dressed in full Ghostbusters gear, coming out to the Ghostbusters song, James Cameron mentions the movie and "Tobin's Spirit Guide" during his intro for the Sigourney Weaver tribute.
During Bill Murray's speech, right after he says "But the people I really want to thank are not the living, and not the undead...", you can hear someone in the audience shout out, "Groundhog Day Sucked!"