I don't have many rules. My pet hates are long, rambling comments that seem to repeat ad nauseum what we've been discussing on this blog (and elsewhere) for months if not years.
I like to restrict comments to 300 words, which I think is generous, but it's not a hard and fast rule. If you've got something to say and do it well, I'll overlook it. On the other hand, comments in excess of one thousand words are, frankly, taking liberties. That's not a comment, that's a speech. If it's any good I'll publish it as a guest blog, or I suggest you offer it to someone else.
Another pet hate is "off topic" comments that have nothing to do with the original post or the preceding comments. This is a blog not a message board. It's rude and more often than not it kills the thread.
What else? Oh yes, I can take criticism but I won't be stalked or bullied on my own blog. And while I welcome comments from all sides of a debate, I won't tolerate personally abusive comments aimed at people who, for example, choose to smoke. I like a good argument (preaching to the converted was never my thing), but this is a smoker-friendly site and I won't tolerate intolerance.
Btw, if you are going to have a pop at me or anyone else, have the courage to do it without hiding behind a fake name.
My favourite comments are those that are short, informative and entertaining. If you remember that I'm sure we'll become good friends.