There is a company that does this. They were very successful in Japan and opened an office in San Jose a few years ago - http://1dollarscan.com - be sure to read the FAQ. They can also do OCR on the book content which makes it searchable and possible to do copy/paste. As far as I can tell what they do is the normal graphical scan of a page, and then underlay that with text. When you select over the page it picks up the text, but when you read you see the graphical original.
Note that they destroy the books in the process of scanning them (spine is cut off) and then they dispose of the books to avoid copyright and similar issues.