A pretty fair argument against HTML Email
The following snapshot from my Gmail inbox is an aesthetic cautionary tale (click to enlarge in a popup window):
Never, ever, ever, ever assume that a funhouse font like Comic Sans is going to result in an effective impression on the receiving end, especially at 32 points or so. Comic Sans might be the worst font that ever was. Even Nancy refuses to use Comic Sans.
Please, please stop using Comic Sans. Anywhere. Everywhere.