If this has already been posted please ignore. Microsoft announced that in Windows 8 when users are using the new "metro" interface in IE 10 there will be no plug-ins allowed.
This will mean that there will be no way have Unity run in a browser even if the unity project is compiled to flash because flash will not be allowed either. The only good news is that it sounds like there will be the option of using the "old" IE interface and having plug-ins. If Metro is the default though it might become increasingly difficult to rely on plug-ins. Since I do mostly browser development in Unity this was hard to hear.