I'll be the one 'no vote' on the autographs for a preschooler. After one character encounter, DD was totally into seeing all of the characters. She met Jasmine first and was a little star struck 1) because she was a Princess, 2) because she was beautiful and 3) because I sprung Jasmine on her (I snuck out of our lunch at Marrakesh and found Jasmine out on the street with no line at all so I grabbed DD and took her out without telling her why we were out there!!) Anyway, after that first encounter, she was really into the characters and had a great time interacting with them. I'm not against the books, and autographs, but I think it was much more memorable for DD to tickle Goofy, to tell Peter Pan and Wendy that she had seen their play at our local high school, and to play peekaboo with Eeyore's ears, than to hand a book to characters that have great big mitts on their hands and can barely scratch out a legible semblance of their name for a kid too young to read it anyway.
I know this sounds harsh, and I am not against other people having the books, but I think they take what is an opportunity for one's child to have a unique interaction with a character and turns it into more of an assembly line. DD had a card that she wanted to show to Woody, and since I think it is probably hard to hear from up there in Woody's head, he misunderstood that she was trying to show him the card and he got his own pen and signed it. Not that that was a bad thing, but she didn't get why he signed his name to it.
DD is pretty perceptive and saw other kids books, but when she asked what they were I said, "some people think it is cool to have famous people write their names down for them" She nodded and moved on.
Just my .02 on the topic. I'm sure that the books are helpful for shy kids who still want to get close to the characters. I am willing to bet that we will have a book with us on our next trip, but for our first time, I am glad that DD had more time to play and we'll get the autographs on a return trip, if she wants to.