Honestly, as an end user, there's really not much difference between Flex/Flash and Silverlight, so I can understand your hesitancy.
From a developer's point of view, I think Silverlight offers some very compelling features. It uses .NET, which means that's one less thing you have to learn and that much more knowledge that you can leverage. This also means any .NET language can be used: C#, F#, Visual Basic, Visual C++, or even IronPython or IronRuby. It is reported to be a superior solution for video streaming, which is why the few big applications the public has seen it in have focused on that.
Check out Silverlight's own Showcase for some views of what is possible:
Showcase : The Official Microsoft Silverlight Site
As far as a Mobile version... All I have to say is, no matter when it comes out, it's been long overdue.