Displays a single line textarea for entering comments, users can press "enter/return", and comments are loaded and submitted via AJAX.
Make sure that "Anyone can register" is checked in "Settings --> General"
Users can add their "url" or "email" by clicking the "more" link next to the textarea.
At the moment it does, Google Ajax Crawling will be added in a later version.
At the moment no, later versions might.