Miguel de Icaza is writing yesterday on his blog that he wrote a Silverlight plugin for Linux:
"The past 21 days have been some of the most intense hacking days that I have ever had and the same goes for my team that worked 12 to 16 hours per day every single day --including weekends-- to implement Silverlight for Linux in record time. We call this effort Moonlight. [...]"
Have a look at the screenshots or the Moonlight Project Planning Page.