If you like to flip through The Unbound Book (my book art photoblog), then I have treat for you. There's a photoblog over on Tumblr that records and explains scanning errors from the Google Books project. It's called The Art of Google Books.
You can see one example at right. Someone inadvertently hit the scan button while they were flipping the page.
I've just now found the blog, but it's been around since April of last year. It now has 15 thousand followers, so I wonder how I managed to miss it.