An to add to this meta-comment: Remember that someone might have read your post and replied, even if you haven't seen it yet, because you hit "reply" - saw that you needed to do an obvious edit (because there is no preview).

It's sometimes frustrating when you've just realized that you've made a bit of a fool of yourself in the heat of the moment (or in your non-idomatic use of English, and come off as more of an ass-hole (or just more rude) than you might have intended, as might be the case for those of us whose native language isn't English...) -- and then having to explicitly acknowledge in a "edit: whoops, didn't mean to be offensive, sorry"-comment that you did in fact post something a little foolish, rude or just silly.

But, with the high rate of view/replies to some hn-threads, it's better to be safe than sorry, and add a small "edit:"-comment whenever you edit -- even if it's just formatting, grammar or spelling.