This is a big deal for shops like 10th Magnitude, my employer, especially given that we developed the API for Arrow Payments. PCI compliance means banks—who have skin in the game—have certified Azure is secure enough for credit-card processing:
The PCI DSS is the global standard that any organization of any size must adhere to in order to accept payment cards, and to store, process, and/or transmit cardholder data. By providing PCI DSS validated infrastructure and platform services, Windows Azure delivers a compliant platform for you to run your own secure and compliant applications. You can now achieve PCI DSS certification for those applications using Windows Azure.
To assist customers in achieving PCI DSS certification, Microsoft is making the Windows Azure PCI Attestation of Compliance and Windows Azure Customer PCI Guide available for immediate download.
The latest Azure release also has a bunch of other great features for developers, including monitoring tools and Web site improvements, but PCI is the big one.