I believe is something related to HTTPS: go to gmail.com and wait for it to the several redirects it performs. Before getting to the login screen, Safari nightly gets stuck at the url stated. Something similar happens when getting to other HTTPS sites that include redirects: for example, using the HP Online Shop (hp.com) or Outlook Web Access (Exchange 2000 Server). It's not security settings related and also tried using other browsers and work fine... Hope this helps.
I can access GMail, the hp store and my work's OWA (though it's Exchange 2003) all fine using my locally built copy of r30758. Does this happen in shipping Safari or only with a nightly?