I was not very impressed by Visual Studio 2008 and could see no compelling reason to upgrade from 2005. But the Visual Studio Rosario looks like it is going to be of major benefit to serious development centres. It has much better support for Architecture and Design, improvements in it testing capabilities for test teams as well as historic debugging and production debugging from a USB drive.
For more on Rosario check out this video http://channel9.msdn.com/posts/Dan/Doug-Seven-Visual-Studio-Team-System-2008-and-Rosario/
