I wouldn't feel comfortable using something like markdown until I had a firm grasp of how it works and the kind of html it writes.
And at that point, I guess I might as well write good ole html... Unless browsers _universally_ supported a new better language, I'd hate to have to think of browser nuance in two different markups...
I use Markdown when I'm writing content-heavy prose, like wiki pages or READMEs. When I need more control over the exact classes and tags, HAML is a good alternative to HTML.
In the case of Markdown prose, I don't /care/ what kind of HTML it writes. Headers, paragraphs, links, all taken care of. I write text, it gets run automatically through a parser/html generator (I use maruku), and I don't think about it. HAML is great for templates & layouts, when I care about DIVs and ids and classes, without being the wordy, ugly HTML itself.
And at that point, I guess I might as well write good ole html... Unless browsers _universally_ supported a new better language, I'd hate to have to think of browser nuance in two different markups...