I use HTML in email from time to time. I have scripts that generate small business reports (sales, basically) and use HTML to tabulate them, and then send that report in HTML form. The audience is business people, so they don't want a "table" made with monospace-fonts, and it would be overkill to attach a CSV or something like that.
Ideally I would have a general purpose webserver where I could have my report hosted (or generated on demand), and just tell people "Look here when you're interested", rather than spamming them. But I'm not expecting a miracle!
So anyway, as a /.er I am of the "plain text email only please" mindset, but I'm in the minority in my organisation and must adapt.