@Franco I disagree with portraits of women with the 85 vs. 50 mm. In fact, some of my best shots are at 200 mm head-and-shoulders on my T2i. The compression of the facial features is quite noticeable that far away and most women tend to find the results quite flattering. Most guys? ... probably don't care. If you're shooting out-of-doors the narrower field of view of the telephoto also tends to help make the background disappear so the subject pops out of the picture.

Obviously, 200mm is really too long for candid street photography.