On the ArcGIS resources site, the descriptions and most of the functionality sounds pretty much the same. What are the benefits and downsides of using one over the other?
I was told by ESRI staff that the ArcGIS API for Flex will no longer be in development, but I don't see that anywhere officially yet.
However, Flex uses actionscript and MXML to create and requires the Flash plugin to display.
Silverlight uses C# and other Microsoft languages using Visual Studio I can't remember and requires the Silverlight plugin to deploy.