In one of the keynotes of the Microsoft PDC 2010 or 2011, Top-manager Ballmer, or Sinofsky , or someone else, said that IE9 was so important to Microsoft that they will put a lot of effort into the IE9 release. They were thinking about "forcing" users with IE8, i.e. Vista users, to upgrade to IE9.
He also said that "selected Windows 7 technologies" will be bundled with the IE9 installation (so you cannot install IE9 and IE8 side-by-side). I wonder which technologies these are? Is IE9 a substantial upgrade, or kind of a "hidden" service pack for Vista?