I just heard this morning that the Google Books app is no longer available through iTunes, and after some digging I can confirm this is true. Google Books is no longer listed in iTunes.
Curiously enough, the app running on my iPad still works. I fired it up and I can still read all the ebooks including the couple I bought. The app still has the link to the Google eBookstore website, too, which is probably why Apple pulled it.
Interesting. I really expected to see this sooner.