My kids are 5 and 3 and autographs were definitely the highlight of both of our family trips. We went in April '05 and were very surprised at how much both kids loved the characters. DD then 4 1/2 loved the autographs and DS then 2 1/2 loved the characters but didn't care about the autographs. We just got back from our second trip and DS now 3 HAD to have his own autograph book. We used books of spiral bound index cards that came in different colors. I then put the autographed index card below the picture of the kids and character in a photo album. A fun alternative if you're not into scrapbooking. I also make journal entries on these cards and insert them into the photo sleeves.
We did spend tons of time in character lines and even waiting around for characters to show up, but that's what the kids really wanted to do. We got more than 50 autographs and met around 60 different characters. The kids LOVE to look at their album.
We did spend tons of time in character lines and even waiting around for characters to show up, but that's what the kids really wanted to do. We got more than 50 autographs and met around 60 different characters. The kids LOVE to look at their album.

My thoughts exactly. Getting the book helped my older dd when she was 4, so we got one for our younger dd at 2.5, and for both, it was a way to interact with the characters without having to think of something to say or hug them too soon.
The books were great for character meals and the odd character we saw without too long a line, but they won't cause you to fall into the mad quest for autographs trap, unless you want to. 
The next day at animal kingdom, we figured out that a lot of kids were having books signed so we bought one for DD4. DD2 was afraid of all characters in costumes so we didn't get one for her. But this year I think we will get one for her.