We're already starting to see some cool samples that use Silverlight 2 really effectively. Prior to MIX, we had a small private beta running to get some early feedback on the builds that we were producing, and a few folk made really good use of this time to build some interesting ideas out.
This one is one of my favorites: TextGlow is a Silverlight 2 application that reads Word .docx files. The Open XML format is an ECMA-ratified standard, and having a web-based runtime with the power Silverlight makes it possible to accomplish something that I don't think you could do easily with any other technology. TextGlow downloads Word documents asynchronously, opens them as ZIP files, parses them with LINQ-to-XML and then renders them using the WPF-based text and graphics APIs.
This is a big deal, and not just because it's a cool Silverlight sample. In years gone by, if you wanted to share a document on the web, you'd typically have converted it to PDF format (assuming you had the full version of Adobe Acrobat on your system). Having two versions of the document meant changes were hard: you had to reconvert the document every time you made a change or the PDF file wouldn't match the current version. TextGlow solves that problem by providing cross-platform access to the source Word document, regardless of whether you have Office installed on your machine or not. The version of TextGlow above is a demonstrator, but there's endless potential for this. I hope the SharePoint team is watching, in particular.