I've recently published a code sample showing how to implement a Mediator design pattern in Silverlight 2.

In my implementation three loosely coupled Silverlight applications are hosted on the same page and communicate with each other by raising the events which trigger actions in other Silverlight applications subscribed to these events through Mediator. Separate, possibly invisible, Silverlight application could serve as a Mediator or, as shown in this sample, Mediator could be one of these applications interacting with each other as long as others know its name. Mediator doesn't have to know anything about other Silverlight applications communicating through it but merely expose and register itself on the page.

This is a screenshot showing three Silverlight objects and navigation elements: 

This sample is compatible with SharePoint 2007 and can help in implementing Mediator design pattern with SharePoint web parts.

Please find the description and a source code on CodePlex: http://www.codeplex.com/SilverlightMediator . I would be very interested in comments and suggestions on where this implementation could be used.