What the Hell has Linux got which Windows Lack?

Public Support. Especially of the people who know the difference.

I can think of a few reasons why a common PC user should install linux. As people have already stated the cost is a major one. You can download a linux distribution for free. Linux is now a user friendly operating system. A few years ago it was a little complicated to use. But today there are plenty of high quality distributions around. Windows in my opinion is just bloatware, filling your hard drive with features you don't want and probably won't use. And if you upgrade to the newest version of windows you'll probably have to upgrade half your hardware as well. Personally I'd rather install something like linux-xp, which is capable of running Windows applications, and spend the the cash saved on purchasing vista on something more usefull.