Markdown seems to be part of the retro/hipster trend, along with flat UIs, 8-bit video game music, fixie bikes, and Pabst beer. As someone who actually lived through the 1980s, it's amusing to watch you young cats reinvent my youth.

I'm not saying Markdown is a bad idea, but I'm perfectly happy using the rich UI provided by a word processor when I write. Next thing you know, someone will claim that 80 characters max per line was a great idea, and there will be a little iPhone app that rings a bell when you get to column 75 so you can hit the carriage return in time. Non-skeuomorphically, of course.