At the MIX 08 keynote ..
.. or if that fails, http://sessions.visitmix.com/
.. it was announced that Silverlight is being installed by Internet users at a rate of 1.5 million installations per day.
I think we can now pretty much rule out the question as to whether Silverlight is going to reach critical mass enough for it to not be "weird" if you expect your users to download Silverlight before using some widget on your site. I wouldn't have cared, because I knew better, were it not for having to work with co-workers who beat their chests in pride and remain intentionally oblivious to the sheer significance that Silverlight brings to the web on the whole, even now.