https://market.android.com , the books tab allows Android OS phones and tablets to access Google eBooks readily and quickly.
Google eBooks are also available on PCs, Macs, iPhones & iPads, Nooks, Sony Readers, and more - supporting virtually every reading platform.
In addition to current popular books, Google eBooks added thousands of free public domain titles - spending the last few years involved in the Google Library Project wherein they scanned and converted thousands of public domain titles from large university and public libraries.
Perusing some of these free editions, I find that while the text block itself formats quite well to google's browser-based reader and looks well enough that I would consider reading a book at my computer screen, I find the legacy artifacts from the library notations on various pages to be distracting and annoying. Yeah, Google preserved thousands of books and saved millions of hours by not re-typesetting them but using OCR and scanning technology instead.. but I find myself preferring a Gutenberg eTexts
For professionally formatted or restored books the Google eBooks format is great - fast, flexible, and attractive to look at on any device. For scanned books - bleh.. but, in the cases where the book is available no other way, I guess you take what you can get...