Nah, a meteor is much too quick of a death and not nearly painful enough.

But if Microsoft did just up and disappear I think it would be awesome for computing and for world economies. At first everyone would probably panic, but people do that all the time anyway. After the initial screams, stampedes and such died down people would realize that they could still get a hold of copies of Windows 2000 and Windows XP and that those two should be plenty good for at least another couple years.
People buying new computers would start migrating en masse to Mac's, but not all of them because there are an awful lot of Intel boxes out there that wouldn't just go away, and Intel/AMD would still be around to make new processors. So, in the next couple years the Linux community would kick it into high gear to give the world some decently-user-friendly software to run on Intel boxes. This would result in massive investment and development in the technology sector.
Apple might decide to port OS X to Intel but Linux would have the jump on them. Lindows would too, and would skyrocket since it can already run MS Office and other Windows software alongside Linux programs.
By the time Windows XP and 2000 were too out-of-date to use, there would be other, better alternatives and a whole lot more Mac users. Compatibility, especially backwards compatibility, would be a prime focus for everybody (to make it easier for people to switch over) and since Apple would have a larger market share it would wield more power and many more programs would be multi-platform and more formats would be platform independent.
Competition between operating system makers would rise to a level not seen for a long time, and we all know what healthy, cutthroat competition can do for innovation. World peace would soon follow, and Microsoft would be safely cast into, well, wherever old operating systems go when they die.
The only down-side to the whole gig would be that we would be robbed of the opportunity to look MS users in the eyes and say "See! We told you we'd win!" because, though we'd have won, it wouldn't have been a fair fight. I am, however, willing to live with that. So if any paranormal or extraterrestrial forces are wondering what I think of dropping a big one on Redmond, I'd like to give them a big, hearty, green light.