A good question - I recently got a "blue dot" and no comment from someone who has 0 posts (wonder if it's the same person?). Don't really know what it's supposed to mean, because as far as I could tell my rep count didn't go down...

I know on some other forums where they have rep counts you don't have to submit a comment for a +rep, but you can't "ding" someone unless you give a valid reason. It might also be useful to prevent anyone with 0 posts from giving reputation. Don't know if that could be implemented here? Where's Man1c M0g when you need him?