The current Silverlight version of the Photosynth viewer is built in Silverlight 2. Moonlight 1 is an implementation of Silverlight 1 which was mainly good for building media players that worked across platforms but will not run Silverlight 2 apps. Moonlight 2.0 Preview 1-7 is actually Moonlight 2 Alpha. You should probably bookmark the new Moonlight 2.0 Beta page ( http://go-mono.com/moonlight-beta/ ). Only when Moonlight 2.0 reaches its FINAL release are you guaranteed that the Silverlight 2.0 Photosynth viewer will work for you, although I certainly hope to see it work in the Betas in the coming weeks.
Just remember that Moonlight 2 is still not final until sometime in September. I don't know what will happen for Linux users when the Photosynth team releases the Silverlight 3 version of the viewer this fall. Hopefully the Silverlight 2 viewer will stay available until Novel and friends can complete Moonlight 3.