Microsoft has been inspirated by the best virtualization model, like IBM AIX has and uses Citrix-like service to allow remote access to its locked up applications, after you pay.
You get the operating system, that has been developed *only* to connect to M$.
All your data are stored in virtualized OSes and virtualized applications of M$.
Your box contains only access keys to your data on those boxes, that's why it's so portable.
It's not designed to make you secure, it's designed to make Microsoft's software "secure" in a way of enforcing payments for usage of M$ software.
Software runs on foreign M$ servers, applications accept remote connections and control, that's made by something like Citrix.
There will be no need and no way to download your copy of Office, nor a copy of any other application Microsoft produced.
You just pay per month for online access to it, all your data will be stored online on foreign PCs of M$ and your PC will be nothing, but a lighweight client.
What I described is what I strongly believe and what the facts I found contain.
Slashdot Mirror
http://www.microsoft.com/presspass/press/2007/sep07/09-11VirtualizedDesktopPR.mspx
You can access the virtualized version of Office already today, just download Citrix-client, or wait until M$ makes an OS from it.