N(exactly)FRC: This is the crux of the Google Books settlement...
And it links to the "freemium" theory: give people something for free, and they are more likely to *buy* the actual item. (Bands whose music is pirated the most typically see their revenues rise the most in the industry--but whether this is true for books is another ball of wax.)
There are serious fears behind the Google Books Settlement, though I would argue that anyone excited enough to find these books online would probably look into purchasing an original copy.
(There's a lot more to it, and I'm not an expert by any means, but it does raise some interesting questions.)