Miti was very busy this summer and if you read his article you can see why. If you want to integrate your Flex application (web or AIR) with PayPal his article on this matter is a must.
In this article, I will show you how to integrate PayPal Express Checkout with either a Flex application running in Flash Player or an Adobe AIR application. Express Checkout streamlines the checkout process for PayPal buyers, but there are security implications for using it in stateful applications.
l will review the security and UI considerations, introduce the architectural approach, and then show you how to implement the whole thing. You can also download working samples to see how everything works together.