An anonymous reader writes with this quote from a story at El Reg about an early look at the Silverlight 4 beta:
"There are ... major changes to Silverlight's out-of-browser functionality, a loose equivalent to Adobe Systems' AIR runtime for Flash. Even when fully sandboxed, which means having the same permissions that would apply to a browser-hosted Silverlight applet, out-of-browser applications get an HTML control, custom window settings, and the ability to fire pop-up notifications. ... Unfortunately, some of these features are not what they first appear. The HTML control in Silverlight 4 is not a new embedded browser from Microsoft, but uses components from Internet Explorer on Windows, or Safari on the Mac, which means that the same content might render differently. The HTML control only works out-of-browser, and simply displays a blank space if browser-hosted. Clipboard support is text-only in the Silverlight 4 beta, though this could change for the full release. More seriously, COM automation is a Windows-only feature, introducing differentiation between the Mac and Windows implementations."