Talk about weird, I just posted about the login screen being found and now I noticed that the service is live! Just go to the Google Notebook Homepage. Time to start tinkering around!
UPDATE: Firefox 2.0 testers need to use the Firefox extension link above otherwise Google will say you are running an incompatible browser. If you use the direct link to the extension above you will be able to override the settings manually using the Nightly Tester Tools.