Rusty has setup a nice page that tracks the Moonlight 1.0 status with various applications out there. We are using this as part of our QA and development process.
As it turns out, it was easier to support .NET-based Silverlight (1.1) applications than the Javascriped-based ones (1.0) as the .NET-based ones tend to do all the heavy lifting in managed code. And it was very easy for us to use tools like corcompare to ensure API completeness.
With 1.0, the story was different, we were debugging things on a when-we-find-a-problem-we-fix-it approach. JB recently created a tool based on the Microsoft specifications that helped us close the gap quickly. We went from hundreds of missing entry points to less than a dozen in a week.
We now have cute Firefox installers for 1.0 and 1.1 on Linux/x86 and Linux/x86-64, once we have the new codec framework in place we will make them available to the public for testing. In the meantime, people interested in testing Moonlight still need to build it themselves. See our Mono Olive mailing list for details.