As you know from Visual Studio 2010 Ultimate you can perform Load Testing as part of the software life cycle management.
The only problem were when you want to perform Load Testing for more than 250 Users, in previous versions of Visual Studio Team System – There were no User Limitation, in 2010 you had to buy Visual Studio Load Test Virtual User Pack 2010 in order to increase the amount of load users (Each pack allow 1000 Users). – Visual Studio Load Test Virtual User Pack 2010 page
Today Microsoft Announced – Visual Studio Load Test Feature Pack
Available to all Visual Studio 2010 Ultimate with MSDN subscribers. With this feature pack, you can simulate as many virtual users as you need without having to purchase additional Visual Studio Load Test Virtual User Pack 2010 licenses.
So if you have Visual Studio 2010 Ultimate with MSDN you can unlock the Users limitation and perform Unlimited Load Testing Using Visual Studio 2010 Ultimate!