Is it Time to Ditch Windows?

I've been thinking about getting a new computer for almost 2 years now and due to my indecisiveness, I've missed the boat for one that comes with Windows 7 as standard.
Of course, I could simply install my current HDD into the new computer and keep using the version I've got (although I'm not sure about the legality of that, no one would be any the wiser) but one of the benefits of a new PC is starting afresh without any of the clutter that you had on your previous system.