Since the release of patch 4.0.6, we've been keeping an eye on healers and how they are performing and are currently in the process of making some additional adjustments.
The cost of Power Word: Shield is being increased by 33%. While we wanted Discipline priests to be able to utilize this spell more often and with better results, we also did not want it to be the main spell (and often the only spell) used while in groups. We don't find this to be a particularly compelling playstyle and have found that it encourages players to avoid using other spells such as Penance. We believe that using a shield in a tight moment is totally appropriate, but we don't want it to be incredibly efficient to do so with more frequency than that.
We realize that by making Power Word: Shield slightly more expensive for Discipline priests to cast that it might cause Holy priests to avoid using it. To that end, we are adding mana savings into the Body and Soul talent. The tooltip will not reflect this change until a future patch, however. Ideally, Holy priests should not notice much of a change to the Power Word: Shield costs.
We are also applying a hotfix for Purification for the Restoration shaman passive from 10% to 25%. We think that shaman healing per second is not as competitive with other healers and while we hoped to bring down Holy priest and Holy paladins (in particular) in 4.0.6, which we did, shaman still appear to be behind. In this case, it is simply easier to buff Restoration shaman rather than nerf everyone else or rebalance the encounters.
In Addition - Restoration Druids and Restoration Shaman
We agree with the sentiment among some players that Restoration druids and Restoration shaman are lacking in the healing cooldown department. The shaman buff and Power Word: Shield adjustment above should bring all healers reasonably close in terms of throughput. The decision on who to bring then might end up being dictated by the strong cooldowns offered by paladins or priests. This isn't the kind of thing we can address via a hotix, but it is something we are looking at for the next major content patch.
As always, we appreciate your continued constructive feedback and will do our best to keep you informed of ongoing developments.