As seems to happen all too often with our book recommendations, Looking at Photographs is no longer listed as available new at Amazon U.S. and is listed as "Temporarily out of stock" at Amazon U.K.
Just before I posted the notice below, at 11:34 p.m. Friday, the book was listed at #106,946 in sales on Amazon U.S.; and yesterday by 2:31 p.m. it was #73. I wasn't checking regularly so I don't know if that's as high as it got.
Perhaps Amazon was getting too many pre-orders and wasn't sure if its incoming shipments could cover them all. I still expect the book to be available in the immediate future.
As usual, I'll try to keep you posted. Sorry if you've experienced any frustration or inconvenience.