Just for kicks, I was using Illustrator the other day in Windows, and I had the system monitor open. While saving a file (EPS, 85MB), processor usage peaked at 100% for like 45 seconds, and the memory used doubled, from like 320MB to 650MB. After the 45 seconds, things very slowly went back to normal, with Illustrator using not much more than 10% of the processor, and memory levels stayed at 320MB.
So this tells me one thing. Windows I guess has okay memory management, but it is strange. It doesn't seem to be using the paging file, it just uses RAM to back itself up. Which doesn't seem sane to me, making a backup of yourself in the same place as the original. Additionally, the average PC has pretty slow RAM. My Dell is about 3 years old, and even with 1.5GB RAM, it is slow RAM, so using the base RAM for paging seems hackish - some sort of specialized fastRAM would be better for this. (note please that I'm not exactly a hardware expert, this is just how things seem to be working to me, given the information I have available)
Also, I've done a lot of fudging around with processes in Linux, you know changing priorities and whatnot, and I have never seen a process take up 100% of cpu cycles. Really intensive programs, like transcode, or surface (a mathematical modeler) will spike to 90% at times, but will never have a sustained usage of more than 80%, while everything has equal priority. Giving transcode a nice level of 4 (making it take twice as long) drops this usage to like 40% with no spikes. Interestingly, at this level, the machine doesn't seem to take any kind of performance hit. So a loss of 40% of the processor doesn't make any difference at all to the rest of the computer. While saving in Illustrator, even Freecell will freeze up for the duration.
So what we have here cannot totally be blamed on anything, really. It's a combination of things. Memory management, default processor usage, RAM speed, and etc all play a part. The key, I feel, is the sum total of all the differences. The sum total is that Windows is shit, and Linux is good. The Linux system handles things in a more reasonable and useful way. I dare say that Windows is designed for people fucking around with email and the web and Word, while Linux seems to be designed for multiple hardcore processes - like compiling C, running httpd, backing up files, and fucking around with email and the web and vi.
Again, the effects of these differences aren't apparent in normal secretary situations. But I like to push my computer, having 20 tasks going at once. Windows just can't handle it. Linux can. And my really old Mac can too.