I've been only Linux for a few years and never looked back. I love Linux, it's a Computer Scientists dream OS, not to mention that it also works perfectly for my Linguist parents and a friend as I've converted them too.
It'd be silly to say that it will surpass MS in popularity though any time soon, it's still at a very low usage. And although its fame has been increasing lately I don't really think the increase in users has been significant enough to worry MS at all. The main reason is big companies, which are the driving force keeping MS where it is are really what tips the scales and ne