It proves nothing - Comic Sans is a hot-button, a singularity. If they had used Ariel instead of Courier, would Twitter have exploded? No? It had nothing to do with the effectiveness of the font, it was just a nerd thing.
But that's what we've been trying to find with this article: How Typography affects users.
From the different researches cited in the articles (all backed with data), font selection did seem to make a difference. Maybe Little.