“While called a “service pack”, the sheer number of new features makes this release as significant as .NET 3.0. These include the controversial ADO.NET Entity Framework and the much demanded improvements to C#â€™s real-time syntax checker.
Other features include:
ASP.NET Dynamic Data: This wizard auto-generates database-backed web sites without the need for any hand-written code. From there developers can use it as-is or customize it as if it were any other ASP.NET based project.
ADO.NET Data Services: This framework makes it easier for developers to create REST-style interfaces for querying and update data. A key advantage over Web Services is that is has a URL-based query language is built directly into the framework, eliminating the need to invent a new one for each application.
.NET Client Framework: This drastically smaller version of the .NET Framework contains only the APIs that client applications tend to use. Tools built into Visual Studio will determine if your application is a candidate for the version. This feature is most suited to ClickOnce style deployments where the user is expected to download the framework over the Internet.
This release also includes .NET 2.0 SP2 and .NET 3.0 SP2, which means regression testing is in order.”
Also available : With the release of SP1 for Visual Studio 2008 today, the Silverlight team has also updated their tools for Silverlight 2 Beta 2.
Learn more here