In a Blog entry, De Icaza states that Moonlight1.0 is feature complete, and has passed all of Microsoft's regression testing, and comes with support for Microsoft's Media Pack for both 32bit and 64bit architectures. It can be installed as a Firefox plugin with a single click through the download page.
It is worth noting that Moonlight is fully blessed by Microsoft, and that the Redmond company has helped the Mono team with making Moonlight a reality. "Microsoft has continued to help us all along in creating an open source implementation of Silverlight," De Icaza writes, "They have open sourced the Microsoft DLR, the Microsoft MEF framework and the crown jewels: the Microsoft Silverlight Control Library and the Control Toolkit under the OSI-approved MS-PL licenses. Without this it would have taken years for us to catch up."
Work is continuing on implementing Silverlight 2.0 as Moonlight 2.0, and those interested can build it already.