The edit function
could be problematic. I like the sites that don't let you change what you've written after the fact - we've already got the preview. Discussions/arguments (especially long ones) get very confusing when someone starts editing their posts from the beginning of the thread.
BTW: this post was in no way edited from the original, and then edited again, and then changed back to the original. Nope, no way, nosirree!