This doesn't really count as much, but before I bought MC, I watched MC Alpha playthroughs on YouTube. As for finally buying it.. Well, I actually bought it in November 2012, so I think either 1.4.4 or 1.4.5..
I had bought the game when it was in Alpha 1.0.2_01. Although I was quite bad at the game itself for about a month, I remember how fun it was and how playable it was, considering the content in it was not enough to make my computer lag very often. I can't complain about the game now, it's just basically unplayable for my computer right now.