Well, far be it from me to contradict Ridley, and everyone here knows that I'm not a Microsoft lover - very much the reverse in fact since my "real" OS is SuSE Linux 9.1 and the superb Mepis Linux [
http://www.mepis.org/ ] which I cannot recommend too highly.
Actually it isn't the quality or security of MS products that repels me but Microsoft's attitude and business practices. I'm not going to go into the details (it would take far too long) but the subversion of standards, the vendor lock-ins, the lies, the deceit, the relentless destruction of anyone who dares to challenge their hegemony, the eternal lawsuits that only they have the money to fight and most recently the covert campaign against Linux using the repulsive SCO as a stalking-horse just turn me right off. Nope, MS is a convicted monopolist who wants to own the whole sandbox and won't play nice with the other kids.
Maybe it's because I'm a bit of a nerd at heart but I have to confess that I've had very little trouble with my 2 installations of XP (I didn't have much trouble with 98 either, but that's another story). Of course, I have hardware and software firewalls, adware scanners, malware scanners, antivirus software, snoopers and update and patch things regularly. Not to speak of backups, registry savers and the like. They all run as cronjobs and rarely require any active intervention - though the compulsory reboots are annoying. I run all sorts of apps., including games, heavy duty graphics processing, rafts of free software or shareware and download tons of stuff to try from the Net. Hard lockups? Perhaps 6 in the last year. Bluescreens and Stops? Never had one. Application crashes? Sure - mostly Explorer barfing for some reason. Security issues? Lots of fruitless knocking on the hardware firewall door, that's for sure. Driver issues? Yeah, sometimes (never did get that USB modem working) but a lot less headaches than in Linux. Well, they do say your mileage may vary....
All in all I don't think that XP isn't so bad (though it's horribly overpriced and fenced in by draconian EULAs). From the point of view of OS design it is quite insecure, but that in a way is the price of maintaining the extraordinary compatibility with older iterations and DOS apps. Sure they could have made it more secure, but that would have broken a lot of older stuff and produced howls of indignation.
I can't say much about Macs except to say that any BSD based OS can't be all bad! But I can talk about my beloved Linux and more specifically Linux on the desktop. Linux has pretty much won on the server platform - everyone know that Apache makes IIS look like a pile of poo. On the desktop Linux has arrived at a bit of a crossroads and is having to do a lot of growing up very fast. Hardware drivers are a real pain (of course Apple never has that problem) partly because Linux is newish to the desktop, partly because closed source drivers don't sit very comfortably with the GPL and partly, I suspect, because MS leans on manufacturers who might be thinking of releasing Linux drivers (they've done it in the past and will continue to do it until the DOJ grows some balls and teeth). Application installation, even with binaries written for your distro, can be painful. Windows had DLL hell, Linux has dependency hell. Sure, you can compile source yourself but most people are intimidated by this and it still doesn't solve everything. Red Hat's RPM format is, in spite of it's deficiencies, becoming the norm (sorry Debian users) but package management just has to be made better. Adoption of the Linux Standard Base
http://www.linuxbase.org/ will go a long way towards addressing such problems. Applications? Well, apart from games (and Doom III for Linux has been released) there ain't much in it these days and it's getting better all the time.
The good thing is that all these criticisms are being addressed right now. Every month brings improvements in smoothness, interoperability and ease of use. Sometimes it's hard to keep up!
The worst that could happen would be for MS to release Microsoft Linux! But I don't think they ever will.