there is a fair amount of chatter, even on the minecraft official forums, that Notch is too busy with his millions these days to bother too much sorting the server issues out properly
Having a good game idea, maybe even being a half-decent game developer doesn't mean you know how to write a scalable web-based authentication system. (which isn't hard, but it is a different set of knowledge).
Although I thought they had hired a guy just to do website stuff, but again - if it's been this long - maybe that guy isn't any good at it either. :/