Thanks for a great plugin.
The ability to add your own links to the widget is really good, but it would be very nice also to be able to add custom html. It should work just like the logged_in_links methods.
It will also be useful if shortcodes are expanded in sidebarlogin_logged_in_links (line 143 in version 2.2):
$links = do_shortcode(get_option('sidebarlogin_logged_in_links'));
This will allow other plugins to specify the links or html that will occur in the sidebar. I use this on one of my sites to add extra profile information in the sidebar login widget.