I don't know how long this has been going on, but Barnes & Noble is now doing the amazon.com thing of recommending items based on your purchases. I noticed this over the holidays. You buy, say, “The Book of Daniel,” and they'll suggest another E.L. Doctorow or maybe a history on the Rosenbergs or McCarthyism or the New Left. Their recommendations wind up in your bag along with your receipt. 

Here's the recommendation I got based on Salinger purchases:

YOU MAY ALSO LIKE ...

• Catcher in the Rye by Salinger, J.D.
• Bell Jar by Plath, Sylvia
• Things They Carried by O'Brien, Tim
• Girl on the Train by Hawkins, Paula

The last is a bit of a stretch. Or something.

Anyway, it's a nice innovation ... 20 years late.