Since last night I'm also having problems logging in using Safari.
When I log in to the main page there isn't a problem but when I click on Forums/Puzzles/etc. I get a page saying welcome Guest with a request to login with user name and password (these are already filled in).
I can also see on this page that I'm apparently logged in and viewing the site!
If I then click the login I get a page saying my password is incorrect and giving me the option to change it.
I also get two adverts for Amnesty International on this page.
I have tried to re-enter user name and password, reset Safari, etc. with no change.
I switched to Firefox with no problems which I will use in the meantime.
Thought I would draw your attention to the problem as it sounds the similar to the one we had when Danica Patrick popped up on the login page.