I like the idea of a questionnaire that pops up randomly when making a comment at a rate of maybe 1-10 percent. possible example questions:

• Do you think this comment is funny?
• Do you think this comment is useful to the person you're responding to?
• Do you think this comment is useful to anyone but the person you're responding to?
• Do you think this comment will have positive karma? How much?
• Would you make this comment to anyone's face?
• etc

Displaying one or more of these at a rate that makes you think but not at a rate that would be super annoying would be fun and provide some neat databases.

On the other hand I'm sure programming it would be a bitch.