MSN UK Entertainment are currently testing new MSN v13 UI, complete with Silverlight enhancements. The test site at http://entertainment.next.uk.msn.com/ follows on from the testing of a Silverlight homepage design, http://viewer.uk.msn.com/.
As Peter Bale, Executive Producer for MSN UK mentions when discussing the trial, the addition of Silverlight allows for an improved multimedia experience when using MSN, in particular through embedded videos and images. In addition, once you have signed into MSN, you're giving the option to share you MSN activities through Windows Live, using the MSN Web Application. This is currently hidden in the standard web applications directory, so you'll need to enable it via your MSN profile page, or click this link.