Google eBookstore, a cloud based ebook experience that promises that you can "use just about any device with an Internet connection to read over 3 million books." Books are stored in a Cloud and accessed when you download them to your device (where they are still accessible if your device goes off its wireless connection). Smartly, Google Books can be read on Android, iPhone/iPod/iPad Touch, the Nook and the Sony eReader, as well as on a desktop or laptop. They can't be read on the Kindle but are "open to the possibility" should Amazon allow that. For Android and Apple, apps are available to allow reading on the mobile devices. For Nook and Sony, epub files are downloaded in the Adobe Digital Editions format, and can be manually transferred to these devices.
I downloaded the iPad app yesterday afternoon (after several failed attempts in the morning, due either to high demand or - as the app wasn't even coming up in a search of the app store - possible shenanigans.) I discovered that "My Google eBooks" page comes loaded with several free selections - Alice's Adventures in Wonderland, Great Expectations, Pride and Prejudice (sans zombies). I played with the reader, and then downloaded a sample of Scott Lynch's The Lies of Locke Lamora (the author, along with George RR Martin, that I most want to see in the store of my preferred ebook reading app, iBooks).
As an app, Google Books is perfunctory and serviceable, but the least versatile of all the major readers (Stanza, iBooks, Nook for iPad, Kobo, Kindle for iPad). You can change the font, font size, invert the background to white on black, and (nicely) adjust the "line height" (the space between sentences, what we call the "leading" - something the Nook for iPad also does). But there is no dictionary feature, and there doesn't appear to be any way to link to a website from text. There is a neat feature that allows you to switch between "flowing text" and "scanned text", the latter being an actual reproduction of the scanned pages. I imagine this could be useful when reading public domain works in which the OCR created errors in the text due to mistakes in scanning, but not one I personally am likely to get much use out of.
Opening the sample of The Lies of Locke Lamora, I was disappointed to see that the two maps at the beginning were too small to be legible. Google Books allows you to place your finger over a section of the page to enlarge the text/image, but doing so produced an image so grainy as to be even more indecipherable. So based on this experience, and the lack of the dictionary and other features, I personally wouldn't use the Google app as a primary eBook reader.
Perhaps more interesting is that apart from a "very small" number of titles, once you purchase a book from the Google eBookstore you can download it in PDF and ePub format. Stieg Larsson's The Girl with the Dragon Tattoo is marked "No download files included" for instance, as is its sequel, though The Girl Who Kicked the Hornet's Nest is not.
So first I got a free copy of Moby Dick from the Google eBookstore, then I downloaded it in ePub and added it manually to my iBooks' library in iTunes. The result - a book from Google successfully imported to my preferred reader, wherein I can use the dictionary and other features. Yay!
I then bought The Lies of Locke Lamora as a test. It does allow me to download the ePub file, but in Adobe Digital Editions format, which neither iBooks (as expected) nor Stanza (surprise!) could open. Sadly, I am now testing Google's customer service by seeing how easily I can request and receive a refund.
So my personal take: The Google eBookstore will be a great way to easily procure and read the "millions" of free titles already available from Google, but I personally will transfer such works to better readers, and I won't be purchasing any books from Google since their app fails to break my preferred app order of iBooks, Nook for iPad, Kindle for iPad, all of which are much sexier and versatile reading apps.
However, competition is always good. Already Amazon has announced that they will soon introduce Kindle for the web, enabling users to "to read full books in the browser" as well as allowing "any Website to become a bookstore offering Kindle books." It's extremely likely that the Google app will add features as it goes, and if it adds downloadable epub editions beyond the Adobe Digital Editions versions, I would use the bookstore for commercial purchases. As we all know, it's still very early days on ebooks, and their evolution is just accelerating.