35% is actually a much higher figure than I had in my head. About 12-18 months ago, a Microsoft representative was unable to tell us what percentage of users had Silverlight installed and web estimates seemed to put it at less than 5%. If the 35% figure is true, that's huge growth over that period, and more than enough to make it a serious consideration for shops considering rich internet applications.
I'd like to see some research to back that figure up, because if it's true, it's enough to change our product's technological road-map for the future. We're a Microsoft shop producing premium data products delivered over the web. Creating rich data applications is likely to be far easier in Silverlight (1.0 or 2.0, let alone 3.0) than, say, Ajax, Java or Flash. We couldn't say to our customers "install Silverlight - 1 in 20 people have already", but we can say "install Silverlight - just over a third of people have".