I've seen this one before
I've seen this before at a previous workplace of mine and I've actually conducted a similar experiment myself. We had a number of machines setup and running KDE in Fedora and had the appearance set-up to resemble XP, it was mainly to find out how plausible it would be to move to Fedora instead of XP.
The more tech savvy of the group picked up on it pretty quickly but were quite pleased with how things worked and looked.
It would be interesting to see something similar done by either the Apple or Linux camps and see the results. Theirs would have a more reliable breakdown of numbers and percentages, and should show MS for fools.
Biting the hand that feeds IT
