I posed this question in a post over on itjoblog. There are several reasons why Silverlight struggles to get designer attention, including:
1. Designers are pragmatic and target the runtime that is already deployed most broadly, ie. Flash.
2. Flash is already good enough so why bother?
3. The tools: Adobe’s designer tools are a de facto standard, target Flash, and run on the Mac.
Developer is another matter. The cross-platform .NET runtime is Silverlight’s big advantage; and this time the tools tip the balance towards Microsoft (Visual Studio) – not for everyone, but for the substantial Microsoft platform community. That’s going to be further reinforced by Visual Studio 2010 which gets full visual designer support, plus of course Silverlight 3.0.
Microsoft does have a problem with Silverlight out of the browser. Developers need a way to have these run with more local permissions, subject to user consent, otherwise they will turn to Adobe AIR. Actually the whole Silverlight on the desktop story is confused, since you can also do Silverlight Mesh-Enabled Web Applications, or stick Silverlight content in a desktop gadget or other embedded browser. No, not the one in AIR (nice idea though): Adobe only includes Flash support and the PDF plug-in.
The tension behind this is that ultimately developers and designers need to work on the same applications, so this remains a fascinating contest.