Last week, I added markdown support to a little blog engine I wrote for a django tutorial. And well, I accomplished it in minutes! I like markdown because is really easy to write and generates amazing html. It is presented here and the syntax is explained neatly in Stack Overflow, and they use it, too.
My approach was really simple: I wanted to write the posts in markdown with a preview (like in the question edition in Stack Overflow), store the posts in markdown and display them in html.