I don't know if this is related to the the playfab server issue I've seen mentioned... but I'm unable to login.  In fact, I don't see an obvious "log in" button anywhere.  When I select Play or Tutorial I receive the following prompt: "Warning you are currently offline! If you would like to continue earning gold, please connect to the internet."  When I select Login, I'm dropped back to the main screen.

 

At the top left I have a wi-fi symbol above a green dot with the text "Link Social Gaming Network" to the right.

Saw this is already reported in this thread: http://forums.obsidian.net/topic/86192-login-and-link-social-gaming-network-buttons-do-nothing/