Reading: When to Give Up on a Book

Over at Read Roger, The Horn Book editor Roger Sutton wants to know:

I’m curious to know what rules other people out there might have for Giving Up. (And Fessing Up: how much of a book do you have to have read in order to say that you read it?)

How long do you wait to stop reading a book?  Do you slog on through anyway?

I used to give a book 100 pages, but now I usually give it 50.  I figure if after 50 pages I don’t care what happens, I won’t care after 100 either.  But then there are books where I kind of don’t care but they are interesting enough that I will go on and finish them.  I recently read Queen Victoria’s Bomb, which falls into this category.

I usually don’t say that I’ve read a book unless I completely consumed the narrative.  Sometimes this does involve the kind of dual-level reading though, where while you are sort of taking in the words on the page, you’re really thinking about something else.  I’m never sure how to determine if I’ve fully read a non-fiction book.  Do I need to read all the appendices to claim I’ve read it?  What if it’s got recipes sprinkled throughout?  If I don’t read "Preheat oven to 400 degrees," does that mean I haven’t really read the book?

What do you think?