For 99% of the applications, Silverlight is an overkill and can only be justified by: "Developer X wants to use Silverlight because it is cool.". These implentations I've seen with Silverlight are horrible, drag drop (often not working properly) where a simple button would suffice, animations and transitions that get boring after the millionth time, gradients through all kinds of visual elements wich make the text in them unreadable, etc... 

They are still stuck in the notion that they do, just because they can.

Look at the new Channel9. It doesnt use ajax, it only uses Silverlight for the video and it's freakin awesome!