If you're one to look for "tipping points," news from Bloomberg of the availability of downloadable books from its book search service may qualify as the moment in which the norm was to have an eBook format available for literature. The service itself is nothing to shout about: instead of being able to flip through images of an introduction to Dante's Inferno online I can now view a download of that same book in PDF format plastered with "Digitized by Google" labels and prefaced by "keep it legal" advisories to encourage care as copyright laws vary from country to country. The boilerplate also advises against making commercial use of these downloads, which is somewhat ironic but necessary in the light of publishers concerned about Google's semi-competitive position. Other than that the PDFs are just image shots of a book right off of a library shelf, with all of the little notes, stamps and scribbles that a volume accumulates through the years. Searching of the PDF is not enabled since it's just an image file, which makes the searchable online versions more useful for research. But if you're dying to have one of these books on your PC or mobile device you're good to go.
As is often the case with Google these features roll out incrementally and individually may not seem to be hugely significant in and of themselves. But in this instance I think that it's important to recognize the breadth of literature that will come into downloadable status automatically as time moves on. As with many Web inventions it's not so much what they do out of the box that matters as much as the net effect of millions of people worldwide becoming used to a format as normal and acceptable. Book publishers are beginning to ramp up for eBooks in a big way now that a new generation of readers migrates to Web-defaulted reading patterns, a trend that is likely to be accelerated by Google Books having made centuries of literature available in that format.