There is a new article on Network World commenting on the performance work we did in the Vista and Longhorn networking stack; there is a nice quote in the article from Ian a product manager:
“The secret sauce behind these tests is the enhancements we have done in the networking layer,” said Ian Hameroff
Check out the article it reads a bit like a paid advertisement but I can speak from personal experience these changes make a huge difference especially moving around large files on my home network I get MUCH better network utilization now that were all Vista.