Ghostcrawler, when not directly occupied with the pack of idiots harassing him on the Damage Dealing forums, stopped by the Healing forums this past month to share some information on how healing is likely to change in Cataclysm. Of particular interest is Blizzard's changing design philosophy with respect to what makes healing challenging. Right now tank avoidance is so high that, as GC's previously observed, bosses have to hit like a freight train in order to pose any threat to tank survivability at all. Between that and what's universally acknowledged as the "never running OOM" ethos of Wrath, the unfortunate effect has been healers spamming their largest heals on anyone within range.
The model that Blizzard's looking to move towards is getting a test run of sorts in Icecrown Citadel -- lower tank avoidance, bosses hitting for more reasonable amounts, and -- in Cataclysm -- higher health overall. In other words, we'll be healing for roughly the same amount we're healing now through less damage that nonetheless occurs more frequently. This will lead to a greater risk of running OOM as the encounter progresses if you dump a ton of mana on damage that should have been healed more efficiently. Even now, there are encounters like hard-mode Vezax where you do have to do this, which I thought made for a pretty interesting fight.