Ironically for a community so adamant about data liberation, there is no way to delete your posts or identity. I am surprised there aren't laws to force site owners to allow users to delete their information.
I was thinking the same thing. Twitter, Facebook, Google all allow you to make edits and/or delete.
At the very least, StackExchange-like revisions would be nice. So if something really needs to be rolled back, that's an option.
Just set your password to a large random string...