I have Moonlight installed on Linux, so I checked "Yes" for lack of a "sorta" option. Moonlight seems to be good enough to get to the few Silverlight sites I need (several European TV broadcasters...)
...and not good enough to play the Feynman lectures billg bought and now serves in the Silverlight-only form. I think the reason is that there's no DRM handling in Moonlight. I expect that a lot of Silverlight content will remain inaccessible in Moonlight.
Now I feel less guilty for refusing to install Moonlight on my Ubuntu laptop and downloading Feynman lectures from isohunt torrents instead.
So I guess we can thank Bill Gates for personally financing ("Tuva project: powered by Silverlight") the nice argument to avoid Moonlight and Silverlight: there's still the DRM (not included in Moonlight) to worry about. Even if he fixes the mentioned site, I hope the awareness remains.
I have found that it helps sometimes, but not always, to right click the Moonlight plugin and choose "install microsoft codecs" from the menu.