I was at a Madison Square Garden Robert Plant show, I believe it was the Now and Zen tour, but I could be wrong. Scott Muni, a famous DJ for WNEW FM, introduced Plant to the stage. During the intro Muni said something like, "There is a Zeppelin flying above outside." The show went on, and I think Plant did play some Led Zeppelin songs.
Jimmy Page did eventually came onstage for a few encores and received a thunderous applause. They played some blues standards, unfortunately, no Zeppelin songs were played by the duo.