Cinlee3, yes, Tweedle Dee and Tweedle Dum do sign the books. One of them even wrote "happy birthday to clayton" backwards above his signature!

The only ones we saw that didn't sign were Mike and Sulley and one of the bears, Brer Bear maybe? Woody and Buzz have a stamp of their signature.
Seeing the characters was my DS's favorite part of the trip (11/13 -- 11/19). He couldn't get enough of them! We filled up many, many pages. I was told by many people that they had never seen so many characters around. Now, there were several ones I missed though -- Pinocchio, Snow White. Oh, well! The most magical moment of our whole trip was when my son rode on the carousel on a horse right next to Bert and the penguins. He had this look of awe on his face the whole time -- and never turned away from them. He has seen the
Disneyland Fun video before, and was convinced that he was going to go on rides with Dopey and other characters. I was so glad that he was able to go on with at least one!
I'm not sure where to buy autograph books ahead of time -- but I didn't think they were such a bad price at the parks at $6. I also bought one of their "fat pens" at the park for $3.
My husband had a great idea, I think -- we haven't tried it yet. He suggested we put the pictures of our son with each character (taken with digital camera) on to the sticker paper that you can run through your printer. I'm really hoping that will work! Anyone ever try that?
We saw a lot of unusual characters -- so I was glad I hadn't put the clip art on first. I would not have had a page for some of them. Also, sometimes we were rushed, so it was good that we didn't have to find the page first! Now, granted, my DS just turned 3 while we were down there, so we also had to wheel him over to the characters, get him out of the stroller, get the camera ready, find the book/pen, etc. I'm not the fastest person!
If Overstock.com ever sells them again, buy the signable Mickey and Minnie. They come dressed in natural colored clothing. We took Mickey to Chef Mickey's for my DS's birthday party. Had all the characters sign it -- it was great! We had many people ask just where we had gotten it. Since we had lots of family members there also, I had each one of them sign their name as well. Even our waiter signed it! What a special keepsake for DS! I also had each family member write a little note to him in his autograph book as well.