I only saw it because I was in London for a conference and as one of the evening entertainments we went on a guided walk. The words on St Paul's came as a complete surprise. A colleague and I spent far longer than we really should have done staring at it, and giggling every time the words were about sex. "It's reading our minds!" Not that we were thinking about sex. Or breasts. Though toast was quite tempting. I managed to get photos of SILENCE and something in Arabic. Not breasts.
Anyway, this finally reminded me to go and look up what it was. It's an installation/project/thing called The Question Mark Inside, by Martin Firrell. (See also the blog.) I wouldn't have gone to London to see it, but I'm quite glad I saw it by accident, especially as it's only on for a short time. He claims the words are user-generated, but obviously he's selective about what he includes, and they're not being submitted in realtime. Wouldn't that be awesome, though, being able to txt your word, or twitter it, or something, and see it appear on St Paul's? What word would you txt?