This is so far my favorite feature of the English language. Formal forms in the grammar are a relict of feudal type of thinking and in modern times they are not only redundant but also harmful. Need to choose between formal 'you' and informal 'you' leads to lots of awkward social situations. If you apply informal 'you' to someone older and who you don't know well it is usually a conversation breaker. If you use formal 'you' when speaking with a coeval it may look like you're patronizing him. Women sometimes get offended because they think you consider them older than they really are, and so on.

Also, when you start addressing someone using formal forms it is very hard to switch to informal 'you'. Using these forms affect human thinking and after you have already addressed someone formally (because it was in a professional situation for instance) you are not likely to become friends. In some cultures there is a special complex social protocol for switching from formal 'you' to informal one. This ceremony is sometimes called using a German word 'Bruderschaft' and for some peculiar reason it often involves kissing and drinking alcohol. This, rather unfortunate, photo captures such situation: http://imgur.com/pmf57.jpg

As I find it significantly easier to develop social relationships in English, I often wonder whether this lack of formal 'you' contributes to the economical prosperity of the English-speaking countries (and esp. the even less formal US).