I wouldn't mind it on the home page, or at the end of a book. But I bought a Bible a few days ago from Google Books and every time I open that Bible on the first page I'm reading I have to click on the page to remove the ad before I can begin reading the Bible. That is ridiculous! And I do call that an ad and not a suggestion.
Here is what I get when I open the book:
http://imgur.com/a/Sacg2
If you accidentally touch the ad you see the second image. Again, this is inside of the book and the first page you get when you open it to read the book.