We bought or 4yo son a book in 2002.. he loved getting autographs around the parks, we believe he ould never had approched a character if it wasn't for that reason. We did find he was not too fond of any of the "face" characters, only those in full fur ...
Another tip... On a second trip in 2003, we used the same un-filled book, I simply strapped the used pages with a band of paper, marked it 2002, and it opened to the new section each time, we still have lots of pages for the next trip... so one more band, marked 2003 and then we may get to fill the book.