Slashdot got suckered and picked up a story by NeoSmart which was able to "exclusively reveal that Microsoft's website is in the middle of a redesign that will feature a fully Silverlight-powered interface - doing away with HTML and everything else." The problem, it's all BS.
The sitewide "redesign" was actually just an overhaul of the Microsoft Download Center, something that gets a lot of traffic but is a far cry from redoing Microsoft.com in Silverlight. That's not to say Microsoft isn't using their website traffic to up Silverlight penetration. When the download center launched back in September there was a Silverlight link to it on the main Microsoft.com page. They also featured some Halo 3 content on the main page done in Silverlight for a while. None of this amounts to much of a story.
The Silverlight penetration question is something I'm not sure about. Getting 80%+ penetration is a tough feat to reach. Not impossible, especially for a company like Microsoft, but tough. At Adobe we have somewhere around 8 million installs per day of the Flash Player. Microsoft.com gets about 60 million hits a month, so there's a bit of a discrepancy. Like I said, it's not impossible, but this is going to be a really interesting thing to watch because no one's tried to get massive penetration from scratch before in the "new web".