The patch for Ulduar is imminent. There's no release date yet. Personally I believe it will land sometime this month. Healing assignments has just gotten more complicated. Incoming damage is more than what's currently in the game. To cap it all off, mana regen's been slightly nerfed.
So here's a quick summary of what to expect and how to counteract for it. I've participated in some of the normal mode Ulduar raids and a few heroic mode Ulduar raids. It's tough. The level of complexity and effort required is somewhere along the pre-nerf Hyjal and Black Temple days.
Come to think of it, when I participated in these encounters early on, the game designers felt that it was too easy. So they ramped up the amount of healing overall that needs to be done since the last time I tried these out. Ho boy!
Get used to using these instead of Flask of the Frost Wyrm. Two things happening here are the fact that regeneration for most of the healing classes have been affected in some way and boss fights are expected to get lengthier. We haven't quite returned to the 20 minute Illidan encounters yet.
To help ease the stress, your guild may wish to bring another healer or two.
Expect overall raid damage to increase. It seems that every raid boss is going to have an AoE spell or an effect that will damage the whole raid. The raid group as a whole is going to have to take steps to buy as much time for the healers to get to them. Yes, stay out of the fires. This time around, it's also stay out of the falling snow.
Again, bring another healer. My guild will not be going in with less than 7 healers.
This is where the Priests in your guild will shine (hopefully). I have a soft spot for Discipline Priests (since I play one). Expect bosses who have the ability to two shot your tanks. Having a Priest can increase the odds of survival due to their Power Word: Shields. Instead of being two shot, they'll have to take three in order to go down.
Although a Priest isn't exactly a requirement, I'd say it's a strong recommendation.
Assigning healing isn't necessarily going to be harder or more difficult. It's going to require much more finesse. The closest thing that comes close would be your OS3D encounter. Every healer has a job. Not only that, certain healers have to do certain things at certain times for certain results. Coordination demands will be going up. The brute force healing methods being used aren't going to last very long into Ulduar.
A classic example of this is Kael'Thas in Tempest Keep. That fight was a virtual nightmare the first time I did it.
This should go without saying. At the moment, I'm gemmed for pure throughput. On a good day I'll have ~2900 spellpower as Holy and after raid buffs and consumables. The gems may need to be dialed back down for extra mana regeneration instead.
This is it folks. We've asked for something harder and more challenging. Welcome to year 2 of raiding. Let's hope we're up to snuff.