Wow! What a difference a good UI framework and programming model can make in development.
We have just implemented several new parts of the adCenter Analytics product in Silverlight in our latest update. These features were written much more quickly than in our AJAX implementation, the look better, perform faster, and were much easier to debug.
Here is a deeper look at how we used Silverlight in adCenter Analytics.
This is a bit of an experiment for adCenter. We haven't moved the whole web UI over ... yet. But it has been a great development productivity gain and improved our overall user experience. Given that we can leverage this in a WPF client if we want in the future, I suspect we will push more this direction.