I have a site I’ve just upgraded to the 1.7.0 this morning, everything went fine with that.
I was logged in as SuperAdmin and clearing out some spam members with Member utilities when I got logged-out of the CP. I immediately went to log back in but the log-in page now has the theme missing and I get ‘The username you submitted was not found in the database’. I can’t log-in with the editors password either. The actual site is down as well, just a complete white page.