I came across this search page inside the Google website that was specifically designed to search Microsoft-related sites.
Just check out http://www.google.com/microsoft.html
This page seems to be in existence as early as 2002. It is quite surprising to find a search page solely devoted to searching stuff related to a particular company. But if you consider the enormous amount of information available in Microsoft sites, the exclusive search page is probably justified.
Actually, the results shown are not limited to Microsoft website. It fetches pages from other sites also as long as the content is related to Microsoft. So the results are not the same as you would get using site:microsoft.com parameter in a search.