I've just added PayPal to my UK site as an alternative payment method with pretty good success. Previously I've only accepted payment through my own merchant account.
I've been toying with the idea of also adding support for Google Checkout. It appeals a lot to me to add this so that I can get the Google Checkout stamp on my Adwords ads, and Google shopping listings.
Nobody has ever asked us to pay using either paypal or google checkout. We are B2B so perhaps companies don't use either of those options. I suspect that for B2C sites the amazon offering will be more used simply because just about everybody has a personal amazon account. I doubt many companies do.
The amazon option isn't available in the UK yet though :(
[edited by: Jack_Hughes at 9:56 am (utc) on Sep. 3, 2008]