What gets me to stay is tablet PC support and font rendering. Linux doesn't have an application that comes close to Microsoft OneNote for note taking. I wish that Apple made a touch screen Mac and I will probably switch when they launch one.
The font rendering on Windows blows away Linux and Mac, in my opinion. There is nothing so crisp as Windows standard font smoothing (not ClearType). Linux and Mac look incredibly ugly without subpixel font smoothing or other heavy anti-aliasing. I spent a while trying to figure out how to get Linux to render fonts better and gave up when it required a kernel recompile.
Has anyone here gotten Linux to render fonts well without subpixel anti-aliasing?