In the case of a book the first pages are likely to be significantly better than the rest. An editor knows that once you have invested in reading the first part of the book you are unlikely to put the book down. This means the first pages have to suck you in, and not do anything to make want to quit reading. The most important part is the first sentence as this is often the only part that drives your buy/leave in the store decision.
My informal sampling suggests most people start at first page. They worry that reading the middle or end would reveal a spoiler. It would be interesting to get good data though.
