The e-book revolution continues apace. In the past week, Barnes & Noble announced the introduction of its own electronic book reader – the Nook – to compete against Amazon’s Kindle and Sony’s e-reader. Amazon promptly responded by lowering the price of the Kindle to match Barnes & Nobles’ Nook e-reader price. No doubt, both companies are looking to the holiday season, hoping their products will turn out to be among the few that are “stars” in what will otherwise be a season of tepid merchandise sales.

And now Google has gotten into the fray as well. It has announced new details on the pending launch of its e-bookstore, Google Editions. This is an online bookstore that will deliver digital books to any digital device such as e-readers, laptops and cellphones. Google plans to offer up to 600,000 book titles during the first half of 2010 alone, nearly matching the number of volumes that Barnes & Nobles will be offering with the Nook.

True to form, Google seems bent on taking an idea that is gained acceptance in the market – and then scrambling the deck to create a new set of game rules. In this case, it’s attempting an end-run around Amazon’s and Barnes & Nobles’ proprietary e-reader devices by offering the ability to download books to any digital device.

Google’s hope is that e-readers will eventually lose their luster once books are available for download to any device. But Forrester Research is estimating that ~3 million e-readers will be sold in 2009 — ~1 million higher than its earlier estimate. And some observers think that Google may be underestimating the importance and value of the proprietary e-readers; they note that Kindle users have been highly satisfied with the product and how it performs. (Besides, the audience for reading entire books on a cellphone device is probably pretty limited!)

In Google’s program, publishers will set the price of books, while Google will earn over half of the profits and share them with its retail partners. But there is an aspect of Google Editions that might turn out to be a significant “negative” for at least some users. Google is toying with the idea of including AdWords or AdSense advertising in its book offerings. Cramming a bunch of advertising surrounding the book contents could be a big turnoff. Even having blue-highlighted links in the text — while normal and expected when reading an online article such as this NonesNotes blog post – could be a major distraction when plowing through the contents of an entire book volume.

Regardless of how things play out, it’s clear that the ~$150 million e-book segment is going nowhere but up in the coming years, and it will be interesting to see how each of the key industry players ends up faring in the coming months. (And the story line gets even juicier with reports that Apple is also nosing around this market and may have something important to unveil before long.)