I have to agree with some of the other posters, Windows 2000 probably was Microsoft's best creation. I'm an OS X and Linux guy, but sitting down at a Win2k workstation isn't a completely horrific experience -- well, unless the install is more than a year or two old, then it starts acting goofy, or not functioning at all.
The problem is, M$ will eventually quit supporting 2000, so people comfortable with it will be forced to upgrade to whatever the latest offering is -- which will probably be DRM hell.
Let us not forget though that Win2k's stability isn't necessarily attributed to M$, but to Digital's VMS, which contributes a great deal to the foundations of Win2k.
Oh, and to the poster that credits Bill Gates for widespread computer adaptation, I think that's totally off base. If anything at all prompted the average individual to buy a computer it was the Internet, something that Gates had nothing to do with. In fact, there's the infamous quote of Gates where he essentially brushed off the Internet as nothing major.
The Internet aside, I'd give Commodore, Apple, and to a certain extent Atari credit for the introduction of PCs in households. They were the first to present friendly machines at reasonable prices, that easily did tasks the average consumer needed. The c64, to this day sold more units than any other system in the world. In the 80's, Gates could give a shit about making computers friendly; his whole "computer in every home" campaign was PR and nothing else. Gates' nose follows the scent of money wherever it may lead, and providing services to businesses makes much less money than controlling every home in America.