In preparation for the Longhorn Meetup, I've been playing with Xamlon ... fun times.
The product shows a hell of a lot of promise ... I mean, we won't have Longhorn for a few more years, and with the delayed adoption rate of large corporations, I probably won't have it at work until 2010! Unfortunately, I've grown quite fond of the whole XAML methodology for writing applications. I feel very at home with the declarative style of the UI markup considering my web background.
Sadly, the fact that they're only in beta right now, and that they have such a monumental task before them makes the product rather hard to use. There are lots of elements and/or properties that have not been implemented yet so lots of the Longhorn xaml samples don't work (after conversion to xamlon syntax of course). How I yearn for Avalon3D support in Xamlon!
If I were them, I would focus on trying to get this thing to run on Mono, as that will likely be a great market for them (assuming Mono doesn't shrivel and die, which is doubtful).
Good luck Xamlon dudes!