I just posted this on microsoft.public.windows.developer.winfx.avalon:

I realise it is very early days in the evolution of Longhorn and Avalon.
However, if Avalon is truly a pillar of Longhorn, surely we should see more
signs of core pieces of the OS taking advantage of it as the primary display
technology.  Currently there seems to be a mixture of IE, COM listviews with
the odd bit of Avalon mixed in here and there.  Can we expect to see
applications such as the Shell, Outlook Express etc fully utilizing this
"pillar" in the B1 timeframe (complete with native Avalon toolbars, native
Avalon listviews etc)?  This will be my measure of Avalon's readiness for
serious app development.

I'm also interested to see which way Office goes - will they go Avalon native or stick with a (deprecated) Win32 UI?  Much has been made of how Outlook will be able to make use of WinFS but little has been said about UI maters thus far.