The SharePoint 2010 SDK is just been updated ! You can find it into the Microsoft Download Center.
The announcement was given by Randall through his blog.

The SDK includes the following new features:

• New code samples:  Silverlight List Viewer, plus new samples in Business Connectivity Services (BCS), Enterprise Content Management (ECM), and User Profiles and Social Data
• Updated documentation, including: new and updated How To, reference , and conceptual content
• Updated IntelliSense XML files for tooltips and auto-complete in Visual Studio

You can find the complete list about this update, for SharePoint Server 2010 and SharePoint Foundation 2010, here:

- What's New in the SDK for SharePoint Foundation 2010
- What's New in the SDK for SharePoint Server 2010