This is such a huge thing, I felt like I had to mention it here:
Unlimited Visual Studio 2010 SP1 Virtual Users with the Load Test Feature Pack now.
Check this link for the details. http://www.microsoft.com/visualstudio/en-us/products/2010-editions/load-test-virtual-user-pack/overview.
This means where other load testing tools charge based on Virtual User licenses, Microsoft is providing these as an added benefit to those with Visual Studio 2010 Ultimate / MSDN Ultimate subscription. All the more reasons to adopt Visual Studio 2010 Ultimate as your primary Load Testing tool.