Bob wants to learn how to program. He has an old crappy computer that's worth 50 bucks with windows ME and he doesn't want to pay $150 for a new windows windows CD and spend 2923 hours downloading 5 gigs of online windows updates with his 24k dialup modem. Bob needs linux.
Bob is a poor student that gets an old laptop for college. Bob buys a $100 laptop from his friend. Bob notices his friends laptop has a 5 gigabyte regedit export and decides he should start fresh but doesn't have the original window CD. Bob installs linux with open office and does all the word processing and essays he wants without ever crashing.
Susy Fookentard is chatting with her boyfriend on AIM while her Windows task manager process list has 190 applications running. Susy wonders why her computer is running slow. Maybe it's all those cute toolbars and that dancing stripper. Susy isn't 'like that' she doesn't play games. She looks at pictures, cam whores herself, and chats all day while listening to music. While she chats about how she can be a fashion designer, Dady's fast 2.5 dual core processor is hosting 80 ddos zombies, and 33 trojans. Mrs. Fookentard needs a Mac.
Bill likes compatibility when he buys the best and greatest hardware in pieces and assembles it himself. He doesn't know how to write device drivers in C. He likes playing insanely graphic direct X based games. Bill has a very fast connection to download all the updates he needs and he knows how to manage what's in his startup, what processes should and shouldn't be running, and that Norton Anti-Virus is really a disgusting piece of software. If something is running slow, Bill knows how to check which processes are using too much memory or if and make sure no unauthorized connections are passing to the internet (with netstat -b). Bill is ready for Windows
Everyone running windows should know how to check for unauthorized connections, notice any suspecious processes (or know how to use hijackthis and forums) and disable startup items /windows services. If you don't eventually you'll have a mess in startup and a bogged down computer from so many disgusting processes and services. Otherwise, with a fully updated windows 2000 or XP, windows runs pretty good =).
Why are there so many darn viruses on Windows? It's not that the multibillion dollar company hires bad programmers, it's that almost everyone uses windows and they have as many lines of code as they have money. The scope of their product is several times more than apple and linux combined. Usually it's not hackers, as many clueless people who've had their computer ruined claim. It's usually people who fall for too good to be true solicitations and download viruses, trojans, or just stuff their computer so full of startup programs and third party services that it's unusable.
Don't use norton. Ever. Update your hosts file. Memorize what programs do what in your process list.