PVE healing style that fits meI generally enjoy druid-healing. I've always - or at least since BC - thought that a good druid healer is a godsend to any raid. While they're not able to keep up everyone alone, on any encounter where a large part of the raid often take damage, they can ease the damage taken by spreading out their hots. A druid healers' throughput when they've got hots running everywhere is rivaled only by paladins spamming glyphed Holy Light through their beacon, if all of it is effective healing. Paladins are also the only to rival druids at overhealing. Can't stop the hot from ticking even if the target has been healed up, after all.
Druids also make good tank-healers. With 3-5 hots rolling and glyphed Nourish to cover spikes, they've got solid tank-healing.
I also like the fact that Nourish with Nature's Grace and Nature's Bounty has so good throughput while still being a short cast when massive healing is required.
Another good thing for PVE healing is Barkskin. It can when properly used help them staying alive through large bursts.
Druids lack any buffs which gives a good reason to stack several druids, like shamans and paladins can provide a bigger range of buffs when there are several of them available. They also lack any kind of damage reduction ability on the tank, such as Pain Suppression and Hand of Sacrifice, so they've got to heal through it all. Nature's Swiftness + Healing Touch is the closest thing they've got to an emergency button. It's not too bad, but it lacks the scaling of Pain Suppression and the like. However, they're the only healing class with a battle res, which can in some cases enable you to avoid the wipe despite losing a tank or something earlier.
All in all, I believe I'm fine with their PVE healing.
Potential as PVP healerWell, reading at arenajunkies.com, it seems druids are not in that bad position. They're generally regarded as the "outlasting" healer, as opposed to disc priests who are better fit in arena teams where the goal is to win in less than a minute, max two.
In battlegrounds/Wintergrasp/world PVP, they have the advantage that they can away from most fights. Particularly if they're healing, then they usually have a decent range from the action when they start noticing things go bad and run. Innervate is also awesome for mana regen.
What I don't like with druids in PVP is two connected problems. One is that their healing and survivability potential is tied to staying in tree-form. They have a rather serious arsenal of crowd-control abilities, but need to drop tree-form to do anything apart from healing, which in most cases means at least a 10% drop in healing done until they return to tree again and a drop in damage mitigated = easier to die. The other problem is that I feel a resto druid seriously lacks dps. Granted, healers aren't "supposed to" be good dps, but they're really only beaten by holy paladins in the "bad dps" apartment. It's very handy in arena that the healer can put out some dps when you need to burst someone down. Besides, doing dps as a druid healer destroys any advantage they have in mana-conservation over other healers.
Conclusion: Druid healer PVP is not my personal favorite.
Potential as ranged dpsThis is a less important demand, but I consider it an advantage if I could have a dual-spec healer who can also do ranged dps. I can do melee dps with my DK if I desperately want to. To be the best healer I can be, the optimal situation is to have two healer specs, one PVP and one PVE. However, since I'm not doing anything cutting-edge, I'd stick with a PVP healer spec and use that for PVE as well. The difference isn't that noticeable for anything below serious raiding.
Ranged druid dps translates to boomkin. Hm. Getting good balance dps is highly dependant on squeezing the maximum benefit of Eclipse. And Eclipse procs randomly on Wrath and Starfire. I left Frost because I didn't like the proc-watching, and this isn't much better.
There's also another reason why I don't want to be boomkin. I've yet to meet a single boomkin in PVP as my DK that actually posed a serious threat against me in 1 vs 1. Of course they are dangerous if left alone, but their dps is nada and they can't keep me off as long as I'm focusing on them. I use Anti-magic shell to go immune to Nature's Grasp, Death Grip to stop them from Cycloning me after Typhoon, I interrupt any of their nature spells with Mind Freeze, and got Strangulate for any kind of emergency or just chain it with Mind Freeze to really stop them from casting spells. Their instant-healing (Rejuvenation and Lifebloom) isn't strong enough to keep them alive for long, and I'll stop any attempt to use cast-time heals. I can see how they can pose a threat if they can live through my initial arsenal of shorter cooldowns, in effect with a healer to back them up. However, they'd be terrible with a healer in arena. If I'm sticking with my DK on top of them, I can stop a lot of their dps.
So... ranged druid dps is not my cup of poison.