While Silverlight may be storming the gates to provide a more liquid and more graphically appealing user interface for .net and SharePoint systems, there are still a few quirks that need to be worked out with Silverlight on its own. 

Primarily in that similarly to Flash, there does not seem to be an x64 compatible plug-in for Microsoft Internet Explorer x64 browser.  Of course that begs to ask the question, what are the compatible browsers?

So what are the system requirements?

Hopefully, in the near future with Microsoft transitioning to a pure x64 platform, I would hope that Silverlight and its competitors are able to produce plug-ins that run natively in 64bit mode.  Could be a bit of a wake up call to all the developers out there that have written custom Silverlight apps in 32bit on the x86 platform.