Longhorn isn't going to be quite the Longhorn we had thought it was going to be.  Faced with looming deadlines Microsoft has had to make some dramatic changes to the Longhorn goal.

So where are they at? For one, WinFS is not going to make it into Longhorn.  It'll come in later.  This being one of the big additions to Longhorn is going to be quite a blow.

The second big change is Avalon. Avalon is the part of Longhorn that third parties have particular interest in as it includes the new compositing engine that could allow users to customize the Windows GUI in ways previously unthought of. 

The good news on Avalon is that it is going to be made into a separate piece that will be able to be installed on Windows XP and Windows 2000. The bad news is that having it become a separate component means that if they don't make their milestones, it too could become like WinFS and be delivered later.

What worries us about putting time constraints on Avalon is that it'll not be done the way it should. If rushed out half-assed, you could end up with something that ends up a "one size fits all" solution.  Where third parties would have to do incredibly hacky things in order to be able to really make use of it.  I'd rather see Avalon come post-Longhorn than to have to write drivers or something to be able to get in there and make use of the Avalon features.

This is especially true if it's going to be something that can be later installed on XP and 2K ala .NET.