Patrick Logan makes an interesting point about Longhorn and the related set of technologies - MS has chosen to make a break with the current platform:
The interesting aspect of this issue is exactly that Microsoft has avoided inflection points of this magnitude so far, but with Longhorn they are *creating* their own inflection point. Let's just watch how they play this out; Longhorn is probably more interesting from a business sense than from a technical sense.
It's going to be interesting to see how this plays out - it seems to me that MS is betting on a reaction similar to the DOS/Windows 3.1 play - they hope that LongHorn will be seen as the place to be, and that anyone on older technologies will be left behind. I'm not entirely certain that it will work out that way this time around - one could easily have called the entire PC space an "early adopter" space circa the early 90's; it's not like that anymore. We are well down the mature market road at this point - witness the difficulties MS is having getting people to move from Win95, Win 98, and NT 4 to Win2K and XP. In theory, that should be a very much easier sell. The fact that it's been a tough road shows you that MS can't just shout "jump" and expect everyone to echo "how high?" It's a different market - one in which there's a real chance for competitors to horn in. If the perceived migration cost to LongHorn is high, then Mac OS X and Linux are going to get real evaluations.