I've bought this game a few times:
-once from a pirate (unwitingly)
-from the HumbleBundle as a gift
-from Steam as part of a bundle
-and today, to get the DevCD

So... anyone taking bets as to how many times I will buy this again?

Same here. Pirated it back in 2003, and I played the heck out of it. Every new patch, every new mod released back in the days was an excuse to dust my digital folder and play through the game all over again. I finally redeemed my old pirate ways a couple years ago when it was added to Steam with Darwinia, DEFCON and Multiwinia. I bought them all back then, although I had no real interest in the last two, and I bought them all again last month on GOG for some extra DRM-free-ness. That game gave me countless hours of fun, I'm guessing we should be even now.

Pretty much the same for me. Pirated the Linux version 2003 or 4 and played it a bit.
Bought the Introversion Bundle when it was on Steam.
Bought the Humble Introversion Bundle for the Demos and Source Access and gave the Steam keys to my brother.
And (hopefully) finally bought it on GOG when it came out for the Developer CD.
I really love that game, would have bought it back when i first played it but it was too expensive and to complicated to order (I would have had to organize a credit card first i.e.).