The ad on the login page of the mobile site was at the bottom of the screen. When I clicked in the user name field and the keyboard came up, the ad moved and covered up the password area which was half the remaining real estate. It took me a few tries to get it out of the way so I could paste my password (my password is like 20 random gibberish characters so I can't type it). A bit frustrating. Not sure if you can just remove the ad on the mobile login page or not.