I finally gave in and have enabled Markdown for comments. We use it as the default text filter for entries, and it’s just a dream to work with.
Here’s a quick tutorial on it, though I can tell you that the biggest thing you’ll use it for in comments is to preface a line with “>” to BLOCKQUOTE something. Like this:
This is some text >This text should be quoted This is some more text
Bulleted lists are handy too:
* This * is * a * list
But this isn’t the place for all that — go to the tutorial and the Dingus. HTML still works in comments, with the tag limitations specified on the comment form, so you don’t have to change anything if you don’t want to.