I could rant about why this is important and add my own commentary around why it's probably one of the boldest moves Microsoft has made, but you'll no doubt be reading a lot of this from others on the interweb.
I will say, that RIA is a concept best built with partners and an eco-system surrounding it. If there are developers world-wide attached to the Silverlight Runtime chances are there will be an entire partner ecosystem to support it. The Novell/Moonlight deal is one of many examples where it's about what we do with the technology, but what others do with it as well.
The Dynamic Language Runtime (DLR) is but an example of this, and this is why I believe Silverlights best days are still ahead of it.
It’s great to see Microsoft supporting the Linux platform as having true cross-platform support does include all 3: Windows, OSX and Linux. Nice to see them embrace the work of the team over at mono-project.com
Next step, distribution 🙂