I remember we had a thread a month or so ago about the windows xp multitasking limits. I did a little test of my own, and found similar results, that xp will run out of resources after having around 60 windows open. I ran the test on kubuntu linux, had about 150 terminal windows open, figured there was no end in sight so gave up. I didn't have an OS X machine at the time, and now I'm not going to bother trying with my powermac g4 with around 400 mb of memory.
My thoughts have always been that for the casual user, windows xp will do the trick. For people who use their computers for productivity, mac os is the way to go. Finally, for people who are not necessarily using their computer as a tool to accomplish other tasks but are really in it for the computer itself (i.e. nerds*), Linux is the way to go.
*This term is not being used derogatoraly; I am a computer engineering student myself!