Underground New York Public Library, and it features snapshots of people reading on the NYC subway. Sarah and I agree that we find this site equally cool and creepy: I will readily cop to the fact that I am a bit of a book spy myself, and enjoy seeing what others are reading. It's the posting photos of readers without permission part that we find a bit dubious. And apparently, we're not alone: one reader-turned-unwitting-model commented "Hello! I am the girl you photographed reading A Vindication of the Rights of Women two weeks ago. I was shocked when a friend sent me a link. (And a bit creeped out, too, I must admit.)" But she went on to express support and appreciation for the blog, so in this case, I guess, no harm no foul.
The site, which also features people using their ereaders on Fridays, reminded me of this old post of mine about the anonymity of digital books, and how they have been a boon to the readers (and sellers!) of genres some readers prefer to read under cover, so to speak. (50 Shades of Grey, a title many readers might feel uncomfortable reading on the subway, was recently the first Amazon Kindle book to sell over a million copies.)
So go ahead: release your inner book voyeur, and see what you think. And for you multi-lingual types out there, there's an additional level of spying: the site regularly asks for translations of non-English titles!