Book Lust: Recommended Reading for Every Mood, Moment, and Reason - Nancy Pearl
"I live by what I call "the rule of fifty," which acknowledges that time is short and the world of books is immense. If you're fifty years old or younger, give every book about fifty pages before you decide to commit yourself to reading it, or give it up. If you're over fifty, which is when time gets even shorter, subtract your age from 100 - the result is the number of pages you should read before deciding."