Last I looked, Apple have a <7% share of the OS market, which is just short of inconsequential. Vista already tops that with 7.91%. Linux doesnt even make it into whole numbers.
Actually, it depends how you break down the numbers. Last I heard it was just over 8% overall, but that includes home and office. There are some estimates out there which has Mac well over 30% of the home market, in the USA.
One thing you may not know is Apple is gaining market share, while M$ is actually losing market share. There is a very real chance M$ can be toppled.
Where are the gamers going to go? Mac? Linux? Great, if you like 2D flash style games...
I think you are a little behind the curve. The library of games for Mac is much bigger than it was in recent years. Now not even talking about bootcamp or VMWare, most games can be made to play through Wine on either Mac or Linux. While Wine is still a bit unwieldy, it is getting better. The day is coming that gaming is no longer an excuse to use Wintendo. I use Ubuntu exclusively now and almost never boot to the XP partition.