My collegue Thijs wrote about Microsoft Silverlight and created a demo to mimic his Pong Clock. Click here for the demo (pre-alpha quality as he says, Silverlight 1.1 alpha required).
Mike Harsh wrote a Silverlight application named 'SilverlightPad'. The idea is based on Microsoft XAMLPad, a visual editor for XAML. Click here to see SilverlightPad in action or here to download the source code.
Another interesting Microsoft project is Popfly. Popfly enables users to build sites and mashups (application that combines content from more than one source into an integrated experience). Popfly is developed using Silverlight and AJAX. Check it out here!
By the way, support for the Opera browser is also underway 
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