Ask HN: Anyone have experience with Amazon's Flexible Payments Service (FPS)?

I often read threads here on HN where people compare the various online payment services, and I never seem to hear anything about Amazon's Flexible Payments Service (FPS). They claim to be 'the first payments service designed from the ground up for developers', but I figured if that is the case people around here might recommend it more often.

Anyone have experience with it or stories to share?

The Amazon FPS web site: http://aws.amazon.com/fps/