Thanks to Ian (you know who you are) for pointing me to the Microsoft.com Operations team blog - specifically The Tasty Morsels Found In Dogfood...MSCOM OPS Top 10 Changes in IIS7.0 post.

Their post goes into detail about the changes they have encountered having upgraded 78 of the 80 web servers that host microsoft.com to Windows Server 2008 Beta 3 - they left two web servers at Windows Server 2003 for comparison.