To be frank, I don't sell very many ebooks via Google Books. I give away about 6-10 copies of The Sixth Discipline (free almost everywhere) every month, through Google Books, but it has been a while since I broke double digits on annual sales.
But what's amazing is, where the books go. Through Google Books I have found readers in the US and the UK, but also in Poland, Lesotho, Indonesia, India, Myanmar, the Philippines, New Zealand, Colombia, South Africa, and Romania. That's amazing! My words have traveled a lot farther than I ever did.