You can't count pre-gui pcs because let's face it, to the home user a pre-guied pc was an over-priced novelty.
When the mac classic came out and the first real gui was introduced is when computer useage stopped being a novelty and started to go mainstream. All the other computers at the time were glorified toys compared to what apple had to offer.
Acorn would be the exception, but that system went over as well as beOs.
I know people are really fond of some of those older systems but atari computers were computers like a speak and spell is a word processor.

And despite that fact that they were such terrible machines (and I would go so far as to say terrible for the time too) they were very highly priced for what you got. They just didn't seem highly priced because the apple pcs of the day cost that much more. They were fun, you could write little bits of code to make them beep or make a pong game, but they did little more than that.
Like it or not, by the time the gui was a given in computing it was down to macs and pcs. If macs would have won our computers today would be 1/5th as powerful and 5 times as expensive. And that's not because apple makes bad stuff, it is because their marketing strategy has always been to hold back new tech until the current tech stops selling and to hold exclusive hardware contracts so that only they make the hardware and thus only they can set the price. Also they design their hardware so that only their software is fully compatible with it.(like itunes and all mac oses prior to X) Wait a second... which one is the monopoly again?
I think I've proven my point.
You really only had two choices. Be thankful m$ won.
And something youki said holds true... it's not really about which os is the "best", it is about which company, and as a result, which os, can give you the most. That has always been m$ since the instant windows 3.0 came out.
Going back to my At&T analogy, although I personally don't have a problem with linux, you can compare linux to one of those jerkwad third party phone companies that sprung up after the goverment broke it up. At&t literally ran the phone lines. They invented the technology. They spent billions of dollars literally making a phone system a necessity in every single home. Now some company that didn't do any of the heavy lifting gets to use at&t's phone lines and at&t's phone technology virtually for free! How is that a fair system? M$'s "big deal" with both ibm and the ibm clones, and the clause that forced ibm to allow the clones to exist is what saved the pc market. We have cheap, x86 hardware soley because of m$'s 10+ years or tireless service. Forget the os, throw the os out the window. M$ made that pc you are running linux on possible. It was directly because of them. Now people are calling them a monopoly because other companies are jealous of their success.
Nobody was complaining when they single-handedly built the home computing industry from the ground up and made the pc a staple for the home. Just like nobody complained when at&t made it possible to call anyone in the united states by literally running the lines, but once all the lines were up and other wanna be phone companies said "hey how come I can't make any money?" so people started calling monopoly on them.
I don't think m$'s "attitude" should even fall into the equation. I'd rather hire a jerk that gets the job done than a nice guy that can't.
Evil has it's place, as do some monopolies.
M$ isn't one, I've already established that earlier. But even when they were, they got the job done better than anyone else could so it didn't matter.
I don't want people to get the wrong idea. I don't think windows is the superior os, I think m$ is the superior company. If people would look beyond the software and look at the things that they really did for the computing industry, they might see it that way as well.
And I'm not even down-playing linux and this new windows clone. I hope they become extremely successful. But don't even use m$'s attitude as an excuse to jump ship unless you are one of those ungrateful types. M$'s killer, take no prisoners, it's my way or the highway, attituse is exactly what got all of the hardware (and eventually third party software) vendors organized and on the same page. Imagine a world where if you switched computer manufacturers upon upgrading, all of your software won't work and thus you have to buy all-new versions. That is what computing was like prior to m$. M$ said "no, you guys are gonna get along and like it, or else you don't get to use our stuff." Thus you get more choices, thus things are cheaper, thus we all win.