Microsoft developed Silverlight to be a competitor to flash (and a development extension for .net, javascript and other languages).

Microsoft is experimenting with search and Silverlight on a Web site called Tafiti, which means "do research" in Swahili.

Microsoft uses Silverlight for experimental search site

I don't think it makes a very good front end for a search engine. However, the XAML (it's like XML) that makes up a Silverlight document can be modified at run time (and re-rendered like HTML -- similar to the innerHTML property) which creates a way to create Rich Internet Applications in a way which Flash (at this time) cannot.