I wonder how feasible it would be to make a markdown sanity checker, to catch common errors, or if it would have too many false alarms. "Are you sure you wanted to make a paragraph with a ton of asterisks in it, or did you really want a list?" etc.

But really, when you make errors like that, it means the markup language isn't intuitive enough. I can never ever remember the proper order for links in Markdown, I hate it. I'd rather have a WYSIWYG-ish editor that both shows your markup (so you can edit it with the keyboard) but also styles bold, headers etc on the fly.