The VS 2010 SP 1 release was simultaneous to the release of TFS 2010 SP1 and includes support for the Project Server Integration Feature Pack and updates to .NET Framework 4.0.

The complete Visual Studio SP1 list including Test and Lab Manager: http://support.microsoft.com/kb/983509

The release addresses some of the most requested features from customers of Visual Studio 2010 like

• better help support
• IntelliTrace support for 64bit and SharePoint
• Silverlight 4 Tools in the box
• unit testing support on .NET 3.5
• a new performance wizard for Silverlight

Another major addition is the announcement of Unlimited Load Testing for Visual Studio 2010 Ultimate with MSDN Subscribers!

The benefits of Visual Studio 2010 Load Test Feature Pack and useful links:

• Improved Overall Software Quality through Early Lifecycle Performance Testing: Lets you stress test your application early and throughout its development lifecycle with realistically modeled simulated load. By integrating performance validations early into your applications, you can ensure that your solution copes with real-world demands and behaves in a predictable manner, effectively increasing overall software quality.

• Higher Productivity and Reduced TCO with the Ability to Scale without Incremental Costs: Development teams no longer have to purchase Visual Studio Load Test Virtual User Pack 2010.
• Download the Visual Studio 2010 Load Test Feature Pack Deployment Guide
• Get started with stress and performance testing with Visual Studio 2010 Ultimate:
  • Quality Solutions Best Practice: Enabling Performance and Stress Testing throughout the Application Lifecycle
  • Hands-On-Lab: Introduction to Load Testing with ASP.NET Profile in Visual Studio 2010
  • How-Do-I videos:
    • Use ASP.NET Profiler in Load Tests
    • Use Network Emulation in Load Tests
  • VHD/VPC walkthrough: Getting Started with Load and Performance Testing
  • Best Practice guidance: Visual Studio Performance Testing Quick Reference Guide