I've been involved in the indie game dev community for a while now, and I was an active member on the TIGSource forums when Markus first presented Minecraft there[0] (he still posted, at the time!)
I remember from day one thinking it would be pretty cool if he could make infiminer with gameplay (at the time, he was talking of a capture the flag mode, and a "defend the castle you built from zombies" mode).
Then he started charging $10 for preorders, which I thought was insane- who would pay money for a prototype that he'd probably abandon within 6 months anyway? (most indie game debs abandon their project- finishing a game puts you in the 0.0001%)
But it actually worked, which surprised me. I finally preordered myself, because everyone was doing it to support him- I think I was order ~11 000 or so. I thought it was insane that he managed to get 10k+ preorders for his small project, and a little something clicked in my head then. Of course, now of over 12 million people have bought the game :) [1]
Preorders were $5, at least by the time I bought (in alpha), which IMO is a much more justifiable price for an impulse buy that might not work out. It was raised to $10 after it hit "beta" (which was after it was already popular and had made at least a million, IIRC).
Even $5 was surprising, as most people on TIGS just post their demos and games for free- back then, most people made games with the only intention of making something cool. It's only recently that everyone builds a game with money in mind, and Minecraft was amongst the games to start that trend (remember, this was before Kickstarter et al.)
http://www.youtube.com/watch?v=F9t3FREAZ-k