EDIT: Forgot to mention. Two good friends of mine do statistical analysis, and programming. Both use Macs; one a Mac Pro, and the other a MBP/15". The latter does a number of development projects, and swears by Mac, and OS X due to UNIX AND the stability/robustness of the MBP. I'll be sure to tell them that they're doing child's work, and to get rid of those toys and get a Vista box...LMAO...
Now that Unix companies like SGI are no longer selling workstations or our of business, Mac Pro's are about the best option if you also need MS office compatiblity. Linux is the next best thing, but lacks MS Office (OpenOffice.org is getting better, but is still not quite there).
Unless you can unbox your machine, download a tarball (or better yet, write it yourself), open up terminal and type make to build an analysis program, you are not doing real computing.
Can you run ruby and Perl without downloading an interpreter on Windows? Nope. How can you do serious sys admin without Perl?
Again, OSX is a great compromise between having desktop apps and the power of Unix underneath.