Tafiti.com - search engine built on Silverlight
Tafiti (or "do research" in Swahili) is a great example of what can be done with Silverlight technology and how it can be applied to enhance traditional applications. You can save and share searches and spin between content (images, blogs, web results, etc):
The search engine technology, of course, is Windows Live
Go to www.tafiti.com and give it a spin