Have they announced how this is going to work with Windows Phone? Apple (and perhaps Google) seem to be driven by the needs of the phone and then the same features end up in the desktop browser as a consequence, but the last I heard Microsoft was re-writing mobile IE based on IE6, which is frankly mindboggling.
edit: Slightly better news straight from the horse's mouth:
Andy Lees: We don't support Flash. Performance on Flash is a problem. So we don't do that. We have Internet Explorer. It's halfway between IE7 and IE8 rendering engine.
Found via the Wikipedia page: