Considering this question about tabnabbing, and looking at both of the demos, located here provided by Sjoerd in his answer, and located here provided by Daniel in a comment, all I had to do was to take a look at the URL address bar in my browser (firefox) and I could see clearly that it wasn't www.google.com.
Is this all it takes to defeat tabnabbing? Or can there be more sophisticated attacks where the URL can be faked as well, to show www.google.com while the page displayed is a fake google log-in page?