Given the fiasco that was Microsoft Vista and the increasing viability of both Mac and Linux, I think Microsoft is on the way out. Their business model was based on buying competitors and copying like mad, and they’ve run out of competitors that are for sale and they don’t have the organizational skill or culture to copy something like Apple’s Cocoa environment or Sun’s ZFS.
Also, @eambos, when you compare Macs to Windows you need to take into account both total lifetime of the computer and maintenance costs. If a $600 Mac mini is powerful enough to last 3 years and a $400 Dell lasts 2, well, you break even right there. And if the Windows machine requires even 2 more person-days of attention over its lifespan than the Mac does, well, there goes that advantage.
And when this generation of college students—which has a far higher percentage of Mac users than any prior generation—makes it into management, and starts asking, “Why are we doing this the hard way, when we could be doing it the easy way?” things will start to change. And when they become management, and say, “Why is it so much harder to do things at work than it is to do them on my Mac at home?” their IT departments will have to change things.
Microsoft doesn’t need a single big competitor to destroy it. Because their success is based on monopoly power and dominating markets, once there’s a viable alternative that 10% of the people are using, they will see their power slip away, and that will be the end of them. Look at what happened with Firefox: MSIE6 had an incredible amount of the browser market share, and web design was synonymous with designing for MSIE6. Then Firefox inched its way over 10% market share, and suddenly Microsoft had to change its tune—which is why MSIE7 and MSIE8 are far more standards-compliant than MSIE6.
I foresee that this will happen with Microsoft Office next, and then that will be the end of Microsoft.