A quick review of this article on Boingboing.
As search result becomes relevant to users need and free preview is provided, Google Book Search will soon become the destination of many book readers.
Soon, Google can take advantage of this and allow searchers to actually purchase the books online directly from Google search results.
In terms of business, this makes way for Google to enter e-commerce and even distribution.
If they do, Google has not and will not compete with portal sites like Amazon, but will go from their core competency: search.
Respectively, competition against Google will not be by search, but on other territories that Google has yet dominated, such as virality and social recommendations.