From the 'may require some assembly' files:

The first 'public' release of Moonlight - which is the Novell led open source effort to replicate Microsoft's Silverlight on Linux - is now available, (though I'm not quite sure that it's production quality yet).

You see the first public Moonlight build doesn't include media codecs by default. Sure you can compile stuff in yourself after the fact - but then again I could also just virtualize Windows and run Silverlight natively too.

Too add further salt - it doesn't currently work on Firefox 3 either. Moonlight developer lead Miguel de Icaza blogged:

Although Moonlight works on Firefox 2 and Firefox 3, recent changes in Firefox 3 prevent Silverlight and Moonlight from working (For details see #432371, #430965). There is a user contributed Greasemonkey script that will work around this bug for some sites (requires Greasemonkey).

So yes Moonlight is out, but it's got a few rough edges and isn't a 100 percent apples to apples comparable technology to Microsoft's Silverlight (yet).

As de Icaza and his team continue  moving towards the Silverlight 2.0 profiles I'd suspect that Moonlight will improve and soon enough become a viable option. It kinda reminds of Mono in the early days, which also didn't quite work as it should in its first few releases but lately seems to be quite solid.