If you've received the message "Your video settings have changed" at the login screen since patch 3.1.2 went live, Bornakk has provided a quick explanation on the official forums:

"After applying the new patch 3.1.2, when reaching the login screen you may receive the message, 'Your video settings have changed.' This is because the Projected Textures option in the Video Effects menu will now default to being turned on instead of turned off."