"U" is the equivalent of "Sie" in German, but the Germans are far more gründlich (thorough) with using Sie correct. It instantly makes you feel more a respected customer.
In middle English and early modern English there was the distinction between thou and you (nominative case; thee and you for the accusative/dative case), the first is familiar and the second is polite. Obviously these days the familiar has been dropped and so indirect idiom takes the place of the honorific.