See Jim O'Neil's post detailing the New, Improved, No-Risk Windows Azure Trial!
Claims-based identity is a simple but powerful way of handling identity and access for your web sites and web services, whether you work on-premises or you are targeting the cloud. You can create more secure applications by reducing custom implementations and using a single simplified identity model based on claims.
Windows Identity Foundation (WIF) is a set of .NET Framework classes. It is a framework for implementing claims-based identity in your applications.
As with any technology, it’s good to understand where the technology has strengths and where it shines.