I've been messing with Silverlight lately to produce a casual game framework for students, I'm using a free set of prototyping images. Its been ok though the way you have to tile lots of images together can be quite inefficent. I prefer the use of a overall bitmap that can be composited together like XNA.
... though that got me thinking, trying to produce a 2D tile based game engine using Deep Zoom, but the DeepZoom control wasn't really designed to handle that much dynamic content eg. items appearing/disspearing, effects, people moving around etc.. So I'm designing my own version of Deep Zoom ...just wait and see people