Our guild alliance is fairly loose about such things, we've let druids tank in AQ40, though not in a primary role, it's mainly a criteria of who's around and who's better at tanking. If we have enough protection warriors who want to tank in a raid, it's better, in my thinking, that the feral druids go to DPS. If we're short healing, we really can't draft warriors to bandage people, so the druids have to pick up the slack.
I've been playing with lifebloom and rejuvenation in healing. I just don't feel that these are efficient uses of my mana regen/healing - too often the ticks are wasted because they're at full health anyway. I'd much rather spend time outside the 5-second window and throw a healing touch that heals the tank from half to full.
Edit: Addenda:
here's my build. It's 28 feral, 33 resto. I'm at level 66, so close to being done; my levelling up is going into the feral side of the equation. I find that with my current gearing, I put out very competitive DPS, around 360 or so when someone else is tanking, and I still heal well for instances.