Our friend Richard Costall wrote an article for SimpleTalk explaining how Silverlight 4 provides additional features, with the introduction of Elevated Trust mode.
Source: SimpleTalk
Richard Costall brought us up to speed on getting Silverlight to run beyond the browser, and now he's giving us a crash course in how to use the new Elevated Trust mode available in Silverlight 4 to give your application even more customisations and permissions on your users' machines.