I haven't decided yet but am considering using Silverlight 2.0 with the next release of Perenthia. I've completed a good portion of my PBBG engine that will drive Perenthia but want to be able to take advantage of some the features of Silverlight 2.0 to provide better user experience. One of the features that really interests me is the socket support for 2.0. Once I get the 2.0 beta 1 bits I am going to start playing around with running my PBBG engine on a socket server application I wrote for Flash. If all goes well I should be able to provide some better multiplayer features in Perenthia such as real time chat and possibly player vs player combat.
Perenthia will still primarily be a text-based game but Silverlight could allow me to bridge the gap between web and client software.