If you are running an eCommerce site that is built on an independent platform, it really does add more value to accept payments via Amazon just like PayPal as an alternate payment method.
Will be interesting to watch if they expand the service to a global market or keep it restricted to US only approach. PayPal's strength is in making it a global play, especially in markets where trust factor / dispute resolution is important.
The experience is okay. Comparable to PayPal, but maybe a little simpler.