An interesting Google feature this one. Certainly a wonderful tool for sourcing any type of book imaginable, but in my experience by no means comprehensive. A random selection from my bookshelves revealed varying results, which probably says more about my taste in reading matter than the effectiveness of Google Books!
As a tool for education, I would say it's invaluable. To be able to source a range of books with options of previews, reviews, full text in the case of out of copyright books and the added bonus of being able to locate the book in a store or library, all from the one site makes it a winner.
Is Google the new Microsoft? Far more learned people than me have many an opinion on what I see as a rhetorical question. But one thought springs to mind... no one these days ever says "do an internet search" or "type it into a search engine" ... what we hear is "Google it!". And with the list of added features growing all the time there is no doubt Google holds a well deserved monopoly.
I've always been quite a fan and defender of Microsoft - their products are top rate market leaders in my humble opinion. They have set the benchmark for many products which companies like Google have then adapted and refaced (don't shoot me!). The big difference? Cost! These products are now available to everyone for the small inconvenience of a few ads. I'm not complaining!