Programmers.SE recently adopted the following policy on comments:
We moderators will now be actively cleaning up questions and answers that have extended discussion in comments: any additional information teased out in the comments should be re-incorporated back into the question or answer, not left as a comment. Any extended discussion should go to our awesome chat system, built from the ground up explicitly for this purpose.
If you see the original asker or answerer leave a comment instead of editing their post, you should edit it back in yourself: anyone can edit a post or suggest an edit.
Because comment deletions aren't very transparent, we will be leaving the following comment when comments are cleaned up:
Commenters: comments are meant for seeking clarification, not for extended discussion. If you have a solution, leave an answer. If your solution is already posted, please upvote it. If you'd like to discuss this question with others, please use chat. See the FAQ for more information.
and the following has been added to our FAQ:
Can I use comments to discuss the topic of a post?
Comments are useful for getting clarifications, but extended discussions detract from the question and its answers. If you'd like to discuss anything related to programming with other expert programmers, please use our chat room.
This more or less reflects the way I've been handling comments on this site, namely that any information important enough to be preserved should be in the posts, not in the comments, but I don't think we've ever really had an official policy on it - that is, comments just got deleted sometimes.
Referring to the quoted post, should we make this, or something similar, an "official" policy on this site?