As of now, you can sign in to the site by using your OpenID. OpenID is a single sign-on protocol which is starting to appear around the web on popular websites such as MySpace, AOL, and Flickr.

For example, I have a MySpace account. If I want to login using it (being if I wasn't already registered), I would use my MySpace URL as my provider URL, and then I would be redirected to a page to login to MySpace and submit some additional information to send back to the website to register me.

That's it, it's that simple. If you're already registered, you don't need to worry about this change.