The first time my DS went, I didn't know about autograph books and we purchased one at the parks, I think it wsa maybe $5? This last trip, I purchased the Celebrations book, and my DS LOVES looking at the pictures that go along with the autographs.
We're going again May, 2007, and for that trip I'm planning on making our own autograph books. I have a girlfriend that did them with scrapbooking supplies and they turned out really cute.
So, in answer to the OP, we do different autograph books each trip.
Have fun!