Ultra fast lenses (F1.2 and larger apertures) are seldom used in street photography, nevertheless it can be a great creative tool in some circumstances. My buddy Kristian Dowling has just written a comprehensive test of these speed kings at stevehuffPhoto.com. So if you are contemplating the purchase of one of these beasts, his article is a great reference to compare bokeh, contrast, sharpness, and colors of rare lenses such as the Noctilux 1.2 and 60mm Hexanon V1.
And since Kristian wrote some nice words about my pictures taken with the 60mm Hexanon V2, I could not resist and post a shot taken with it in Paris last summer. Unluckily (and I understand how absurd this might sound), its value has risen so much that I did not take it along in our move to Argentina. Why risk it in the streets of a country where theft can happen at any block? (click on picture for high res)
Leica M9 with 60mm Hexanon at F1.4, 1/750, ISO160