A few weeks ago I wondered if Power Word: Shield was overpowered, what with all the stacking bonuses it gets in the Disc tree. My reason for saying it might be "too good" was really just wondering if it made sense to base so much of Disc's benefits on one situational spell. It'd be like if 20 talent points in Holy affected Renew.
This week, others are noticing and pointing out how good PW:Shield is. Matt Low (of World of Matticus) posted on WoWInsider about how Disc can use preemptive shields as AOE mitigation. Disc has come a long way if what was once a panic button spell can now be used to pre-shield whole chunks of the raid against upcoming damage. Matt makes a good point that, thanks to Soul Warding making PW:Shield cheap and quickly recastable, this is a very viable strategy. I honestly think that in some encounters, you could do more "effective healing" this way than through Penance and Flash Heal.
There was also a post this week on the WoW forums, by a paladin who was comparing Disc's shielding to pally offerings. Most of the replies were critical of the analysis, but I think the paladin had some good points. Fully talented PW:Shield is a big instant-cast low-cost "heal" that also comes with an energize effect and a haste buff. Plus, frequent pre-shielding (as the WoWInsider post discussed) is clearly helpful in many places in Ulduar. I think Disc as a spec, and Shield as a spell, are very unique and powerful.
The Blizzard reply began, "Power Word: Shield is a really useful tool for Disc priests in particular. We want them using it." It's fortunate that Ghostcrawler said this, instead of, say, "We think Shield is a little too good and we're looking at scaling it back!" I do still wonder if Disc has a little too much invested in one spell, but on the balancing side, Weakened Soul keeps it from monopolizing our repertoire. And I do have to say, now that I've tried it, that the Glyph of Penance does give us a very attractive alternative spell to cast every six seconds!