There's not a single time when I wouldn't prefer receiving plain text instead. I disable all e-mail images by default for every sender anyway, so these little marketing brochures always look like broken messes.
Very good article. I find it's just as important to know this type of "backwards" technology as it is the latest in HTML5.<p>Email marketing is still a huge part of business and it's amazing how many people and companies do it wrong, i.e one huge image, poor support for Outlook, etc.<p>And yes, plain text is easier and more consistent, but it doesn't always work better. A lot of times you're going to get better conversions from sending someone a nicely styled HTML email than you are with plain text.