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.
All of this stands in stark contrast to Lexington High School, which is having a banner year. You may recall that their annual high school musicale featured an alumnus by the name of Amanda Palmer, who co-produced a new play based on the coolest indie-folk album of all time.
For an encore, they picked Eugene Mirman to give the commencement speech: in addition to being good with the funny, he's also a Lexington High School alumnus. (In fact, he was there at the same time as Amanda: their LHS photos, below, come from the same yearbook.)
While there have been attempts to give "the definitive graduation speech" in the past, Mirman comes closest, in my book. (Well, at least he's better than both Mark and Stephen Jay Gould.)