Personally, I do so quite rarely.

If I'm writing something serious I tend to choose my words carefully and think about it a fair bit before I submit. I often edit longer comments for clarity after I've posted them.

Even when I'm being silly, I try to make sure I get things the way I want them, else the joke might not communicate well. Every now and then, though, I look at something I've wrote and I think: yeah, I probably shouldn't have said that.

This makes me a little self-conscious. I don't like making mistakes, especially if they cause misunderstandings, or make someone else's day that little bit less pleasant. That said, if a comment is unpopular and I stand by what I've said, I will do my best to explain it. I consider that quite a different situation.

Overall, I try to phrase my statements in a way that is non-controversial though, unless there's a particular point that I feel needs discussing. Actually, I consider forums like this a kind of learning experience in the way that different people communicate (and interpret things). How much do you think about the words you use, your syntax (word order/phrasing), or the comments you make? Do you ever/often post things that you regret? When do you feel the need to delete a comment? Alternately, are there comments you particularly proud of? What kind?