Nothing I can say about the events of today that B. W. Ventril hasn't already said better. I've only been to London once, for about a week, back in the late 80s. I actually haven't looked at the maps all that closely. I don't really want to know yet if I have any personal history with the sites of the attacks.
Stupidest comment I read today was on Slate, I think, as they over-reached trying to make a point about Londoners' stoicism and sang froid (or as Douglas Adams once put it, their relaxed attitude towards danger) and compared London today to Washington DC on 9/11/01. Which not only ignores the difference in scale but the fact that, unlike 4 years ago, we now unfortunately have a context for days like today.