A few points
Can't remember the specific posters, but:
Why does Flex score a "pro" for an XML UI description language but Silverlight doesn't?
The Silverlight download is roughly the same size as the Flash player.
The Silverlight 3 tools work with Visual Studio 2008 Web Developer Express Edition, which is free.
Silverlight is cross-platform, unless Mac's aren't a platform.
Moonlight 2.0 already includes some of the Silverlight 3.0 features, and it probably won't take them long to get full 3.0 support.
IIS only why, exactly? For the smooth video streaming, which is a feature that Flash doesn't have regardless of where it's hosted? Hardly a win for Flash, then. Plus, I believe MS are providing free Live hosting for video for Silverlight.
I'm using Silverlight 3.0, and for professional development, it's superb. The amount of the .NET framework that is supported is mightily impressive considering the size of the runtime, and it includes key features that a genuinely useful, such as WCF, LINQ and a fair bit of the WPF data-binding model. The (open-source) supporting frameworks that are available from Codeplex, including Prism, the Silverlight toolkit, the unit-testing libraries and others, are brilliant. Prism in particular includes a very useful tool for sharing source code between Silverlight and full WPF projects, allowing for meaningful code reuse. And the third-party control suites from the likes of Infragistics are extensive and highly-polished.
But more than any of that, and a point that is consistently underplayed by knee-jerk MS detractors, is the ability to write your back-end code in so many first-class languages: C#, Ruby, Python, F#, C/C++, and more becoming available all the time. And the architectural model of the application is the same as for .NET Windows applications. That's a huge advantage for existing, experienced developers looking to move into web-based systems.