Best gaming news I've heard in a good while. I don't really care who works on the modding API, Notch or Jeb, but someone had to do it. I *still* haven't been able to sit down and play the game the way I really want to, because the mods I want to use don't all play nicely with each other.
Please, Jeb, give us virtually unlimited sprite and item ID's. I'd rather it doesn't take many months to make it happen, but I'd rather wait than not get it at all. I've been waiting for many months already, with hope kept alive by Notch saying he'd soon take care of modders. Didn't. Happen.
I think this was a smart move from Notch. He wants to be moving onto other things, and if he didn't make this official it would still have happened. Jeb's slowly been becoming responsible for more and more things Minecraft, and he's extremely smart and approachable. Congratulations to him, and I'm looking forward to seeing more from Notch and Mojang!