I'd stay away from the word promise. A lot of the things he's said has the quantifier, "I'd like to", "I might", "I think," or "I'm considering". Everything he says in the blog/twitter or in interviews with those quantifiers should be taken with a grain of salt.
The only thing anyone should really take as a guarantee right now is the Halloween update, with the updates clearly stated.
If we've learned anything from following a game's development (ie. SPORE) we should take most features a dev reveals with a grain of salt, at least until the game enters beta. And Notch has said time and again, that if a feature is not fun or hinders gameplay, it will be changed or removed, which could happen before he even releases it.
I don't really feel bad for him. A lot of people will rage about Notch "breaking promises." There are some who expect the game to be updated all the time, and there are those who are dead set with how the game is now and expect nothing to be changed, just added. Notch ignores these people. If he didn't the game wouldn't progress and he'd never complete it.
Of course, this development process is unique in that everyone has a chance to try each addition to the game and comment about it. It wouldn't hurt to remind him about certain features he's touched upon that we're looking forward to.