I use Firefox exclusively, I have several other browsers installed as I work in web development and actually bother to check compatability with multiple browsers before making sites live. (Unlike many developers I've come acros over the years).
So even though I've probably opened IE on my home machine 4 times in the 18 months I've had it (every tiem was to help isolate a rendering issue) Microsoft no doubt count me as a user of their browser. In a few months when Windows Update insists that I update IE they'll probably also count that as an extra user of IE9. Even though I'll probably never even run it.