He traditionally gave a lecture to the course on chaos, and he did when I took that class in 2003. I wish I remember what he said! I suspect it was something interesting. Steven Strogatz wrote, in his book Sync,
Every time I taught my chaos course, we'd go through the same ritual each year, and I'd come to look forward to it. I'd call up Professor Lorenz and invite him to give a guest lecture to the class. He'd say, with genuine puzzlement, as if it were an open question, "what should I talk about?" And I'd say, How about the Lorenz equations? "Oh, that little model?" And then, as predictable as the seasons, he'd show his face to my awestruck class, and tell us not about the Lorenz equations but about whatever he was working on then. It didn't matter. We were all there to catch a glimpse of the man who'd started the modern field of chaos theory.
Strogatz wasn't at MIT when I was there -- Dan Rothman taught the class using Strogatz's text -- but Lorenz still gave an annual lecture to that class at least as late as fall of 2006. I'd like to think they did the same silly little dance.
