@jk the main advantage macs have right now is that they almost universally have high-resolution "retina" displays; having more pixels makes fonts look better regardless of the rendering tech used.
Honestly, the font renderer used on linux (freetype2) *is* really good; it's just that very few applications use it correctly. Basically nothing does gamma-correct rendering. GTK only recently started doing sub-pixel glyph positioning. At least most folks do use slight or no hinting now.