What will you have on your very own workbench? Apart from the operating system, IDE, mail client, set of developer tools, source control access, your server machines, etc. Microsoft IT offers server storage, roaming "My Documents" folder, self-created SharePoint sites, desktop telephony integrated system (Office Communicator), campus-wide WLAN with certificate-based encryption, online learning system, etc. Isn't it cool?
When you are debugging and want to dig deeper into set of related API the system provides, what will you do? Visit MSDN Library? Or search on the Internet?
But as a developer in Microsoft, you got option 3. Search our codebase! You can find most source code of our released product in our internal source code search engine, check out who write them, what bugs were found, and how they fixed it. It is definitely an exciting adventure to follow the source code of .NET Framework 2.0, understand how they work, and write better .NET application.