On the new Paizo boards, there was a question of more D&D miniatures to be included in Undefeated, and the response was something like...
A lot of people buy the minis, but not all of them play the skirmish game.
I don't know if they have actual demographics on how many people are playing, but I do think that it is becoming more popular. There are people that play D&D minis ever week here.
As for myself, I buy for my D&D game. I have only played a couple of skirmishes. And I may play more, but I don't collect them with the intent of making a better warband.
I like the game... I had a lot of fun playing, but I was surprised on how long it actually takes to run a 100-point game, and it kind of turned me off. And now I see warbands of 200 and 300 points... I hear that all of the tournaments (here at least) end on time restrictions, vice actually scoring the requisite points, or totally disbanding the opponents.
-------------
However, I recently had all of my miniatures maps (including many from issues of Dragon and Dungeon), and I want to run some 50-point gladiator matches (no tiles) on my nice arena map!