Why not ?

Microsoft's own backend is run by a version of Linux (they don't trust their own MS products)
(wishing I could remember the MS url that comes back with a linux screen)

1000's of IIE servers were attacked by Code Red / Nimda and changed to Linux / Apache.
Millions of PC's are attacked by VB worms, and some of the users are changing to Linux.

The estimated growth of Linux users is 25% per year.

AOL have seen that trend, and are trying to buy Red Hat.

Why not Microsoft ? Maybe they will buy another distribution ?