Miguel de Icaza of Novell reports, "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." He's on his way to demo it at ReMIX Paris right now.
I like this quote from the mono irc, suggesting how their Linux implementation can add value to the Silverlight Airlines demo that Scott Guthrie showed: also, we should totally add snakes, time permitting
I can vouch for the fact that Miguel didn't know anything about Silverlight's .NET support before we announced it at MIX07. He was at MIX to do a panel on open-source software, and the night before the announcements Miguel and Dave Winer hung out in the blogger's lounge speculating about what the announces might be (Dave taped Miguel here).
This is a really incredible feat of engineering by the mono team! While porting WPF to Linux would have been overkill, Silverlight is a sweet spot. Congratulations to the mono guys!