Although Windows seems to be continuing its growth in education markets (a sad slide for the venerable Apple stalwart), the scientific community is beginning to become a new battleground for the Mac vs. PC argument. An article from E-Commerce Times quotes NASA scientists, among others, who are finding the power, easy of use, and open-source friendliness of recent Macintosh computers (and OS X) as primary reasons that more Macs are showing up in the scientific arena.
Back in the day when I was at NCSA, we had about an even mix of Macintosh machines and PCs, with the Macs being a favorite of the scientists because of the easy graphical interface. At the time, the primary PC operating system was still PC-DOS, since Windows was still in its infancy, so the Macintosh was not only a novelty, but a very cutting-edge piece of equipment.
Unfortunately, there was a big problem with it at the time. Programming on the Macintosh was a big pain in the you-know-what. We had C and Pascal compilers, but there was no easy way to do computational software, and very little of the stuff written in other parts of the scientific community would run without significant modification.
Today, with OS X, things are completely different. Apple is including a friendly and robust (and highly compatible) development environment with every copy of OS X. To top it off, the UNIX underpinnings of OS X make it very easy to work with for scientists whose main computational engines have also been based on UNIX (even in the late 1980's, our Cray supercomputers had moved to a version of UNIX called Unicos).