If you come to apply to a job, and your resume is Comic Sans, you're wearing torn-up clothes, you haven't had a bath in a while, and your English is sub-par? I'm going to make some inferences about your ability to do the job based on the status signalling you're giving me.
But in this case, the person providing the information is, obviously, the one offering the favor. He is, in fact, providing information that the consumer wants to consume. So it's his complete decision how to do that. After all, he's not asking a favor of the audience, and if they want to discount the information based on a font choice? That says a lot more about them than it does about him.
Reminds me of "eye dialect", where an author chooses to purposefully mis-spell words in order to show dialect and have a more emotional impact on the speaker. Many readers hate that stuff. Sometimes I find it really annoying. But heck, that's art. Man wants to spend an hour telling you about something important, you either get past the font choice or go somewhere else.
Weird thing, font snobs. It's like they don't have anything better to complain about, so they just search around for whatever they can find.
This isn't a bad thing -- the pre-association people have for different classes of fonts make it easier to convey messages in branding and marketing. It makes us distinguish between stories in newspapers and magazines (which we should remember) from frivolity that we could easily forget. With fonts, the medium is a significant part of the message.
But if the font is used by default, you cannot reasonably infer credibility from it. If the whole thing feels less credible or less serious anyway, then it's a status issue.
And now I'll Godwin myself out.
Fun fonts can be serif or sans, and are generally more artistic and ad oriented.
But on paper, with much higher resolution, serif looks more serious.
There is general negativity towards the idea of making assumptions based on appearances; but if we collectively decide that appearance is meaningless, don't we lose the useful ability to send intentional messages using appearances?
ie in this instance, if we stop associating comic sans with silliness, will we then have to <silly>decorate our sentences with XML tags</silly>?
(See also: people who dress in goth clothing then complain when strangers assume they are into goth culture)
It might be related to status, but in that case it's complicated; the low status people are looking for ways to appear high status (avoid comic sans), or ways to make others appear low status (eww, look, he used comic sans), whereas the high status people want to protect the integrity of status; a low status person using comic sans is likely viewed a bit patronizing ('well he's a dev; they don't know any better'), and another high status person would be more likely to be defended for the choice, if not have it outright ignored ('the content is what's important; he was just having a bit of fun').
Comic Sans is an informal-looking font, which means low status. Seeing a high-status researcher using it in front of a relatively high-status audience speaking about a serious, high-status topic… is jarring for many people. On a similar note, I know of a guy who often illustrates his very serious philosophical points with Japanese anime references.
Many people don't like such status dissonance. They literally cringe. I don't, and I suspect Simon P.J. doesn't either. And I don't see why we should: we're the kind of people who care more about the structure of an argument than the clothes the speaker is wearing. This is also apparent in His talk, "How to Write a Great Research Paper"[1, 2]. His counsel is all about readability and engagement, never about sounding serious or important.
[1]: http://www.youtube.com/watch?v=g3dkRsTqdDA
[2]: http://research.microsoft.com/en-us/um/people/simonpj/papers...
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As a last note, I have seen suggested here, and in the Stack Overflow thread, that there are much better fonts out there (Comic Neue seems to be the most popular alternative). But let's imagine for a second that SPJ used Comic Neue instead of Comic Sans. Would that make people stop asking why he's using this font?
I don't think so.