@GregS, DonnyEMU:
Comparing the AmigaOS to Longhorn and its API to .NET ( and especially Avalon - the next one, which can do much more than DonnyEMU pointed out ) isn't really fair :-)
When I saw Longhorn Alpha and the next WinFX technologies in action, it was slugish, buggy, but very nice to develop on (.NET framework 2.0 - Whidbey, etc).
re
Treke
But from the users point of view there is little what you can feel from 1st touch: The UI of Longhorn is rewritten using DirectX (i.e vector graphics, quite impressive), that's all.