I think that at some point, he used to use Comic Sans but everyone got a aneurysm so he switched.

Ha, I remember seeing him talk at a conference in 1991 and it was hand-written transparencies on an overhead projector. Comic Sans is a relief. :-)

Also, to add what others have said, he is one of the best speakers I've ever been lucky enough to see in person: SPJ, Philip Wadler, Guy Steele... good company.

Yep, he once asked if there was anything he should change about this talk - I said get rid of the Comic Sans, but keep the casual feel. This was in 2010. You know that a is talk finely tuned when the only thing someone can think to change is the font!

So now he's using a font that makes it look like he's had an aneurysm? Brilliant!

(I probably shouldn't be making any handwriting/typography comments.)

He had an aneurysm, which caused him to choose comic sans. He had a second aneurysm which caused him to choose that thing he's got on there now.

It's also great advice. I especially liked the part at the end about using simple and direct language and the active voice. This alone makes a paper much easier to digest even if the subject matter is hard.

Precisely because he's that respected, I was surprised at the font choice, which I disliked (it just seems to mean extra mental effort for me over something I'm more used to).

He has said elsewhere, in response to questions about his choice of fonts:

  This is a very funny question, why I use Comic Sans. So. All my talks use
  Comic Sans, and I frequently see little remarks, “Simon Peyton Jones, great
  talk about Haskell, but why did he use Comic Sans?” But nobody’s ever been 
  able to tell me what’s wrong with it. I think it’s a nice, legible font, I 
  like it. So until someone explains to me — I understand that it’s meant to be 
  naff, but I don't care about naff stuff, it’s meant to be able to read it. So 
  if you’ve got some rational reasons why I should not, then I’ll listen to them.
  But just being unfashionable, I don’t care.

he also has enough research experience that it's not taken as unprofessional