Heh, and I thought I was being pedantic with my reward cheque. In my case I found inconsistent hyphenation in a technical term used in the book. I had wondered how to hyphenate it in my own writing so turned to Knuth to see what he did and was surprised to find it inconsistent even within a single volume of TAOCP! He wrote back with a funny message and a cheque for the back of San Serrif. It's on my wall now.
