"Normal" users (i.e. the non-geeks) do seem to prefer HTML emails, and in usability studies, A/B testing, and deliverability reports, HTML emails usually outperform text.
In short, HTML emails are better for and preferred by recipients and senders in all but edge cases.
Look, it's all well and good to say "I'm 1337! I use Mutt, or I use Links!". But let's be honest, the majority of people are not going to use a text mode web browser or a text mode email client.
And this isn't something you're born with, like a vision impairment, so people need to make a website accessible for you. This is a personal preference.
Hence, as much as some of us neckbeards might like to go back to a works where 256 colours was the bomb =), the rest of the world has moved on.
I have dealt with quite a bit of clients and they love to use colors as separation for various degree and scaffolds of conversations.
For now, if I'm initiating an email and do not really need to be HTML, I try to stay with text. For other, I just follow the format the current email thread is in.
If your goal is to distract and confuse people, by getting them to click on your ads and buy your products, then use HTML e-mail. If you want to communicate clearly, then stop worrying about layout & typography and concentrate on the words you are writing.
That's just wrong. Layout and typography are important elements to clear communication.
For me, it's all about keeping some control over technology. I tell a very limited program like mutt what to do, and it does it. This is in contrast to begging an incredibly complicated program like a browser to do something, where much of what it is doing is controlled by invisible embedded code written by people who may be hostile toward me.
That's fair enough, but you are very much in a minority.
It's boring to see everything being reinvented again, just with more color and horrible mistakes.
A quick note to web.de and gmx.whatever who send mails as HTML-only: you suck
I can tell you that on just about every metric - brand recall, clickthrough rates, ROI, unsubscribes - HTML outperformed plain text. There were exceptions, both in terms of types of campaign and types of sender - say, if your list includes lots of Hacker News readers.
We found, for example, that including just one image will increase open rates by more than 50% but I can't find it now. Another article on the same topic is here - http://www.alchemyworx.com/alchemy_worx/2009/newsletter/issu....
Also, text-only doesn't mean monospace. I'm happy to read email in whatever sans-serif font the email client picks, with nice whitespacing.
Fortunately, most e-mail clients support a "show this e-mail in text only" view mode. This means that you can have it your way, and others can have it theirs!
Either you will be sending in HTML or plain text, I feel there shouldn't be any excuse of not attaching plain text version of it.