The guidelines to good commenting!
1.) Be polite -- I understand that discussions can sometimes get heated, and I will let these discussions resolve themselves so long as everyone keeps their flamethrowers on the British setting. Hyperbole is about the most I will tolerate. Posting in such a way as to anger or incite another reader (or myself) will warrant intervention.
2.) Respond to the subject at hand -- If a comment is left on a Mente Materia chapter, I hope it is related to what happened in that chapter or to the story as a whole. Occasional questions or comments may be acceptable so long as they aren't drug out into multi-comment discussions that are not related to the medium that the comments are being posted to.
3.) If the first rule cannot be followed in the comments, I will ask you to move it to private messages or user page comments. If the second cannot be followed, I will ask you to move it to the Stardust forums, private messages or user pages.

I suppose the first and last guideline you can follow is this: If your comment isn't something you would want on your page, or isn't one you would want directed at you, don't post it.

ALSO!

If you send me a message and I don't respond, it isn't because I haven't read the message or that I deleted it without even looking. I often check my messages at work but I can't actually reply to them until I get home. And by then I've forgotten. :S

Cheers!