I'll use this comment to address some questions I'm getting on the demo:
Why not a wysiwyg rich text editor? Markdown is for nerds like us. Comments are for all.
Simple reason is that a plaintext markdown editor was easier to implement. I decided plaintext was "good enough" for the kind of site Confab is intended for. If there is enough demand for this, I'd be happy to look into implementing a better editor in the future. Edit: The current editor has graphical icons for all the rich text features which automatically inserts markdown snippets, so even a user who doesn't know markdown shouldn't have too much trouble using it.