I found this (two friends record hilarious critique of Dan Brown's Inferno in the margins!) a couple weeks ago and proposed that my LDB (long distance bestie, obvs.) and I do the same. I found my book today. It's Mary Higgins Clark's While My Pretty One Sleeps. We're going to mail our books back and forth for highly hilarious marginalia hijinks.
I am so excited! It's great fun so far.
Besties and lit friends of GT, y'all should try it.