Silverlight 4 not only brings in all these features, but also a pile of others.  Interestingly, they seem to be making a direct pitch against Adobe AIR with many of the features.  The new Elevated Trust Applications feature (for out-of-browser apps), enables a host of features typically reserved for desktop applications: Local file access; Notifications API; Full-screen full-keyboard access; Cross-domain policy-free networking; and Drop targets.  Of course, features aside, the huge advantage of the Silverlight desktop approach over AIR is that there is only one runtime plugin required.

At the speed Microsoft is moving forward with Silverlight, Adobe is going to have to start seriously upping their commitment to the Flash platform if they want to stay at the top of the game.  Up to now, they could always give the argument of Flex being more feature-rich, and the ease of adaptation to the desktop with AIR - with both of these arguments now void, and Microsoft firmly remaining miles ahead in the developer tooling scene, Adobe's work is cut out.  They still have greater marketplace penetration with Flash player, but that lead is only going to narrow also.

You've got to love competition!