I may prefer Shadow as my Priest's primary spec, but the Discipline tree has also made a special little place for itself in my heart. When I need a change of pace, playing Discipline is really enjoyable. I probably pay attention to changes to the Discipline tree almost as close as the Shadow tree for that reason. Even if I don't play it a lot, I love it. When they announced a new spell coming for the spec, Power Word: Barrier, I geeked out over it just as much as Matticus, our resident Discipline Fanatic.
Unfortunately, Power Word: Barrier has yet to make an appearance on the PTR, and it turns out that we may not see it at all. It's still a possibility, but that's the extent of it. I can sort of see why they would hold off on it, or even change their mind about it. Discipline has gone through a lot of changes in patch 3.1, most of it a really big numbers game. Discipline is a great tree, and while most players might not 'get' the damage mitigation/prevention thing, it's a really powerful mechanic and probably one they need to be careful with.