I think just a stamped book is not enough.
My car has full history right up to when I bought it. I do all work myself, but i still write it in the book, keep all reciepts, write down when any work is done, and if someone was to look through my folder they would see a lot more info than a stamped book, to me thats service history, and that, to me, shows that the owner was caring enough to do it, then more than likely he/she has looked after the car.
Course as Bear has meantioned, you have to look carefully as getting a stamped book is rediculously easy.