It has been a long standing tradeoff of buying something retail, and ordering online. You pay a lot of money in the store, but it is no hassle. Or you can order online and create an account, expose your email address, enter in shipping, billing and credit card information, then wait a week for it to arrive. Well, the playing field has been leveled again. Instead of creating all of these proprietary accounts, Google offers a checkout API that people can drop into their website.
I ordered a textbook from Textbooksrus.com (and saved $100) in less than two minutes. I added the book to my cart, then signed in to my Google account. I then clicked the purchase button, and everything else is automatically taken care of. Ahh, nice.