One thing that's so nice about Stack Exchange is the markdown preview. You can type in code, and have it instantly rendered to make sure it looks like it should.
The Blogoverflow community blogs do support markdown, although this isn't well-known. Most people use the built-in WordPress WYSIWWGFU editor, which is a pain to use.
Pagedown is SE's implementation of the WMD markdown editor. It's open source, and even if it weren't, SE has the source because they use it everywhere else. It's built with JavaScript, so it should be pretty easy to implement as a WordPress plugin for use on the SE blogs.
I still want a proper integrated blogging platform, but in the meantime, could a markdown preview please be added to the existing WordPress blogs? It would make blogging for Stack Exchange sites significantly easier and more enjoyable.