Microsoft posted a PC v.s. Mac section on their website...

Their reasons:

1) Having Fun - Macs might spoil your fun (I am having fun with Macs)
2) Simplicity - Macs can take time to learn (Windows take time to learn too, it's just depends on which OS you started with)
3) Working hard - Macs don't work as well at work or at school (Apple became most popular brand among US college students)
4) Sharing - Macs don't like to share (I find that Mac sharing is more simple than Windows sharing)
5) Compatibility - Macs might not like your PC stuff (Might be true)
6) Choice - Macs don't let you choose (it's true that you don't get to choose colour, Blu-ray,eSata, but i think the silver is cool enough for me)