I went today as I'm in London at the moment. Good exhibition with some cracking images, very very busy though, felt under a fair bit of pressure to move round quickly as there were so many people going round.
They have made the bizarre decision to put captions and photographer biographies at knee height though which doesn't help!
There's also an excellent short film about street photography and how it's changed over the years, a lot of focus at the end on the whole "security" and "paedophile" things as well.