Funny that that's never been my experience with Flash. Flash sites are horrible and I avoid them if I can, but Flash can socially engineer its way onto my machine through cool little in-browser games, whereas Silverlight just wants to "enhance" my viewing of MSDN.
I think Microsoft's BizSpark site actually requires Silverlight, so once every year or so, one of my machines gets to install it so that I can renew my MSDN subscription and get the latest version of VS.NET. That's enough of a reason for me, since it's something I absolutely can't do without, but I couldn't imagine expecting my users to install it just to visit my website.