See Project 2010 SDK Documentation for the March update of the online Project 2010 SDK.
The pre-release Project 2010 SDK is updated on MSDN. Post-beta builds of Project Server are changed for setting WCF service references and using multi-authentication (where Windows and Forms are both used) with Claims. These issues do not affect the Project Server 2010 beta release.
The topic How to: Use Impersonation with WCF is updated again for the RC release, since the previous update in February.
Update of Impersonation Article and Code for Project Server 2010 in the Project_Programmability blog includes code download with the second round of changes that have been made in Project Server 2010 and SharePoint Server 2010 since the beta release.
Topics with major updates:
Developing Project Server Workflows (all four subtopics are updated, including a PowerShell script for managing workflow deployment)
Prerequisites for WCF-Based Code Samples (includes the corrected changes for creating a PSI proxy)
The managed code reference also has more content, particularly in the Workflow and Driver areas.
The SDK download will be updated shortly after product general availability.