I made a side comment about Microsoft Silverlight on a previous post and foxfier asked if I just don't do Silverlight.
I try not to. It isn't terrible technology. In some ways it's worse than Flash, in some ways it's better. Microsoft likes to say that Silverlight is "based on" open standards because they use XML packaged up in a zip file. Two comments about that: first, it is a terrible way to do things from a technical point of view, and second, it is a trivial sop to open standards given the enormous barriers to competition that Silverlight creates.
Frankly, Silverlight represents an attempt by Microsoft to create an internet platform that they can control. Given their history, Microsoft is not a company that you want controlling any more platforms. Unless you own stock or work for Microsoft, of course. And they don't support the platform anywhere except Windows and (sort of) Apple.
Now, Adobe isn't any better than Microsoft and Flash isn't any more open, but it is, at least, much more widespread on the internet and the clients are available on more platforms. People interested in open standards can copy a single platform more easily than two. So if you have to use an application like Flash or Silverlight, and you care about keeping big companies from controlling technology that they didn't create (which is what happens when a company controls a platform), then you should go with Flash.