YouTube - If you are not logged in, the “respond to this video” textarea asks you to Sign in or Sign up on mouse-over.
/Via Marian Buhnici
iOS - Moving the lock slider from left to right gradually fades out the ‘slide to unlock’ text.
iOS - When “Character count” in iOS is turned on, it will show the character count only if you have at least two lines of text.
/via Bartosz Olchówka
Typinator - Menubar icon dims when you activate password / security form fields.
Apple - Signup form shows a lighter version of input description once you clicked on. Then once deselected the blue border subtly fades out.
Maps - the subtle differences in map designs. See link below for detailed analysis.