Some weeks ago I came by Jeff Webers (aka Farseer Games) small game "We Are Bugs". I thought about if this game could be easially ported from browser Silverlight to a Windows Phone app in Silverlight.
It turned out that it was VERY easy to do actually.
Next up I wanted to challenge myself a little, so I set the goal to port "We Are Bugs" to XNA too.
This part was actually also surprisingly easy and lucky for you - I put that whole thing on Github (as I'm also playing around with Github these days).
So go grab the source from Github and see how a Silverlight game could look in XNA.