Daniel V
while you can style controls with CSS, the nice thing about Silverlight is that you're developing in Windows Presentation Foundation rather than a browser; Popfly is written in Silverlight.
Daniel B-T
When Silverlight 1.1 is available, Popfly developers who want to get into the code will be able to use languages like IronPython and you can already code in Visual Studio or VS Express and use Popfly just for the sharing. I'm with you - JavaScript is not a real programming language in my book. Popfly is trying to be inclusive; my sister could use it to make a custom flickr badge without coding, my Real Programmer friend could use it to share Java apps without exposing my sister to sourceforge...