Following two downloads are especially interesting for developers who build connected systems and use WF, AppFabric and co.
This is a Platform Update to the Microsoft .NET Framework 4 containing a set of new features addressing top customer feature requests and important .NET Framework scenarios.
The service pack for Visual Studio service pack 1 is available too. It adds some support for designing and developing applications for Microsoft .NET Framework 4 Platform Update 1.
You are nor sure if you already have installed updates? Then take a look on this post
If you are interested on Windows Azure development and Windows Azure AppFabric you should download the new April Training Kit.
Read the complete post at http://developers.de/blogs/damir_dobric/archive/2011/04/30/net-framework-updates-available.aspx