There are many people around me obviously I am talking about Windows users, who ask me this question.
I have a very simple answer.

1. I dont have to pay for it and to the various softwares that I use. Yes that is it. I realised this after Abhas Abhinav’s Talk during Mukti [strongest of all for me at least ].
2. I get the freedom to change and redistribute, it may not be important for those who dont code. For them the first reason may be a strong reason.
3. You cant install the same product on two different machines.
4. I feel that INDIA is a poor country ( please dont mind ) and if we cant stop importing hardware we can always stop importing paid software. So use FOSS.

Otherwise Windows is also a good OS, I donot intend to compare Linux and windows here, after all we all have used windows at some point or the other. There are also some very good softwares and games like counter strike which I left playing for my love for Linux. May be some time later I may create Counter Strike for Linux [joking] .

This is my opinion and I am FREE to keep any opinion. You may be against it.