Boris, 50mm is too long for crowded shots. Many street shooters prefer 35mm, or even 28. My 35 (SMC 35/2) is very long, even without its metal hood. A shorter 35, or a pancake (Pentax 45/2.8, Ricoh-Chinon 40/2.8, Ricoh 28/2.8, or Cosina-Porst-Vivitar 40/2.5) with the hood off.
On the other hand, given that an SLR makes some noise, a bit of distance could be an advantage. Around town, I get my street shots with a 135/2.3, my go-everywhere (outside) lens. But then, I don't try to stay invisible.
