When we started thinking about how to bring Java to the Cloud, Spring became an obvious choice as the most flexible and lightweight enterprise Java framework on the market. From the beginning, the Spring framework has been laser focused on letting you write code that has absolutely no knowledge about the container while getting all the benefits of running in a container and consuming its services. This makes it easy to move your code from one Spring container to another and even moving it to a completely different container.
With Google's announcement to support Spring on Google App Engine, Spring developers get the full benefits of this portability having yet another choice of Cloud deployment besides VMforce. This is a really strong message to Java developers that you can deploy to the cloud without being locked in to any one service provider. Our mission at Salesforce.com is to enable all Java developers to build applications in the cloud that leverage and enhance the many services already provided by Force.com. Now, these developers have one less thing to worry about, and I believe we'll see strong adoption as a result.