When I graduated from high school, we didn't even have a celebrity speaker. It was just my friend Mark, who, it turns out, gave a nice speech, so much as I recall. (I also remember his down-to-the-wire grade-grubbing to ensure that he was our valedictorian and not his academic arch-enemy. He beat her after GPAs were calculated down to the thousandths place. I was nowhere near the running.)
When I graduated from college, I had to endure Stephen Jay Gould's natterings, which were so disjointed that the science majors sitting near me were unable to follow what he was talking about. I never went to my grad-school graduation. It was in Missouri. 'Nuff said.
Anyway, apparently Lexington, Massachusetts, has a high school that invites some sort of big name to come talk to the seniors before they're loosed on the world.
This year, they picked Eugene Mirman, who is both funny and a Lexington High School alumnus. And, while there have been attempts to give "the definitive graduation speech" in the past, he comes closest, in my book. (Well, at least he's better than both Mark and Stephen Jay Gould.)