Starting today, you can store your RIA program data in our cloud storage servers. The service is still experimental, and limited to 100MB storage, but this is huge. You can start getting your feet wet today, develop some cool applications, and get prepared for the future of rich Internet applications.
This scenario is potentially game-changing. With a solution like this, you'll be able to deploy rich apps that maintain state, without having to maintain a server cluster. We already have thousands of developers using Silverlight Streaming services to deploy rich client code (which can include .NET code, Python, etc.). Now developers can tie to a powerful back-end data store which supports the entity model using XML or JSON. All without configuring a single web server or database server.
To get started, read the introductory materials or watch the session from MIX07, and create your account. You can build your data model entirely online. You can get support and inspiration on the forums.
I've already created a data model, it wasn't hard. If you build anything cool, send me an e-mail and I might mention it here.