I'm sorry but Silverlight KICKS FLASH'S ASS. This tool is unbelievably powerful. Most of the comments I've seen in this thread have been incredibly vague.
1. If you ignore this tool, it's your loss
2. Proprietary components? What!? It is server agnostic (you can deploy it 100% from a Linux machine). Additionally, it adheres to the standard web architecture, unlike Flash.
3. Silverlight was formerly "WPF/E", however, it is not part of the .NET 3.0 framework.
4. Limiting authoring tools? Nope. All of the authoring tools generate either open text or xml. Pretty damn open if you ask me.
5. Flash blows