The perk wasn't huge, just a star that appeared beside your name or something similar on your Minecraft.net account. It was just a recognition that you bought the game during development and helped said development along. I remember hearing about it when a bunch of people with Alpha and Beta accounts lost their login during a server migration problem. When their accounts got reinstated they lost the Alpha/Beta banner because it was a fresh account.
I'm just having trouble finding reference to either this fiasco or the Alpha/Beta account perk. And when I went to Minecraft.net, I couldn't find anything different about my account (I have a Beta account) compared to a friend's who bought the game post-release.
Am I looking in the wrong place? Or did they take out the recognition banner/star/whatever?