Continuing to work my way through (long overdue) merging of open-source contributions, today we've got another much-requested one that was implemented by @wirelyre: a preview function for markdown.
Anywhere that you're writing markdown now (comments, topics, messages, user bio), there will be two "tabs" above the text field for "Edit" and "Preview". You can flip back and forth between them to see what the result of your markdown will be while you're writing, which should make it a lot easier to work on some of the tricky formatting like tables.
Like so many other features, there are still a few little weird interface oddities with it, but I wanted to get it live on the site and will probably do a few more minor tweaks to it today. Let me know if you notice anything particularly strange or broken with it.
And thanks again, @wirelyre!