Search queries to find Silverlight and XBAPs apps
Silverlight and XBAP serve the same purpose, but in different ways. Both allow for viewing for WPF (XAML) based applications in a browser. Silverlight is a self-contained, cross-browser plugin which supports a subset of the .NET framework, while an XBAP (XAML Browser Application) requires that WPF be installed on the host operating system.
You can get an idea of what people are doing with XBAPs by searching for url's with the .xbap file extension. Microsoft's search.live.com doesn't support .xbap filetype searches yet, but Google does: