Here's what I have learned from my years of experience with computers (27 personal, 17 professional).
Microsoft products are crap. Except Notepad. Notepad is a simple, well written app, and this makes me wonder if Microsoft didn't buy it themselves. lol
Now, I don't mean to stir controversy, but this is my honest opinion. They are bloated apps, chock full of legacy code, usually because it costs Microsoft more to hunt down and remove old code than it does to patch it later. Take MS Office. One of the most bloated products in history. Hundreds of MBs, for what? A word processor and spreadsheet. That's all most people use it for. Most will never use powerpoint (unfortunately I have to), Infopath, etc. They use Word and Excel. Next time you're in Office, hit the "help" button, and see just how long it takes to launch a simple HTML viewer app. I was a system administrator (in one flavor or another) for Windows systems 3.11-XP for desktops, NT-2K3 for servers) for years, and the flaws, bugs, and patched literally drove me nuts.
Why ship an OS with 30K KNOWN bugs and flaws? Because it's cheaper then fixing them now, and after 1+ years of delays already (like w/ 2K and XP), they need that new product out the door!
Now, I will give Windows it's due. It's basically simple to use. The wizards can walk most people (even most computer fearing people) through app installs, simple maintenance, etc. And as long as you install, (disable a few services like the Windows Messenger service), and don;t install tons of crap (like OEM junk), CometCursor, etc, and keep the updates current AND do regular maintenance (defrag, scandisk, etc), you should be ok. If you want to do serious gaming, Windows is really the only game in town.
Now to expose my bias. I'm a Linux person at heart. Toyed w/ it for a few years, now I am a Linux System Engineer and Security Analyst. I find Linux to be superior to Windows on multiple levels. More secure, apps are not as bloated, less bugs in the OS and in most apps, I can custom compile my apps from source code and taylor it specifically to my system (software and hardware combos), no need to defrag the drives, etc, etc. But I suffer in the gaming arena. Sure, lots of new games are either native to Linux now, or run in emulation like Cedega, but not enough. I have yet to have any trouble finding an open source app that does what I want it to do, and have all the same functionality as my Windows box. Except for the gaming ability.
Bottom line, IMO, Windows can be relatively stable, but not completely stable. You will still have the occasional crash, the required reboots after patches, etc. One of the reasons I prefer Linux. I can install most system patches and updates, and not need to reboot.
Ok, I'll stop my rant and STHU now.
