Healing Strategy

A druid's mana pool is already sizably smaller than a priests, and though the instant half and casting time of regrowth is similar to flash heal, regrowth costs a TON more mana, because you are also paying for the HoT half of regrowth as well. 
 
Typically in 5-man's I throw a rejuv first on the Tank when he gets to around 85%-90% and as its wearing off/he drops down to 60-70% I throw on a Regrowth. Throwing rejuv first lets him build aggro and hold the mobs better than if I started with a Healing Touch, at least from my experience. Then depending on whether Regrowth critted or not (50%) I'll start casting a rank 7 or rank 10 Healing Touch. If he's not down to at least 85% by the time I'm close to finishing casting, I'll sidestep/abort the cast, then immediately begin casting again and sidestepping as needed. 
 
I think as a druid the fact that you have TWO HoT's that stack is something every druid should take advantage of. I've found that many times, after you've dropped both a Regrowth and Rejuv on a tank, it's enough HoT to match the damage he is receiving, which means you dont have to cast for a while and can make up a significant amount of mana in full regen mode. 
 
Another tip for 5-manning that I have found to be very useful which is touched upon in the Cat's cower ability. On my main caster bar, as the last hotkey (the "=" key) I bound to a macro that shapeshifts into cat and also targets nearest enemy. Then on my cat bar as the "=" key I have /cast cower(rank 3). 
 
I typically stand back a little ways from the main fray, so if I happen to aggro a melee class, then they will coming running to me and away from the battle, this gives me time to shapeshift into cat, and the shapeshift cooldown to wear off, and by the time he reaches me, I have my cower ready to fire. The macro makes it so once you see a mob come running at you, just press "=" as many times as you can until you see the "!!!" above his head and he goes running back to the battle. 
 
Only drawbacks to using cat/cower is that it won't work on casters and ranged mobs. Cower has a super low radius (5 yards). Also, the target needs to be in front of you for it to work, but this shouldnt be too much of a problem for 5 manning, since most fights are pretty controlled (its the 15 man raids that mobs tend to run around everywhere, besides in 15 man's aggro shouldn't be too much of a problem, there's so much DPS floating around). And the last thing of course is that it only works on single mobs. If you manage to pull aggro from 2 mobs, you will cower the closest one off you, then have to wait a painstakingly long 10 second cooldown to cower again. If you have 10 seconds to wait in battle for a cooldown without your party getting heals, they don't need you there. So I typically pop back into caster throw some heals around and just yell 'aggro!' and if in 10 seconds a warrior/shammy hasnt pulled him off you well then first of all you have a gimped group, but then you can cat/cower again. 
 
Taking a look at the numbers side of things, a Priest's fade costs 275 mana at lvl 60, with cooldown of 30 seconds and lowers threat by 820. Druid's shapeshift costs 55% of base mana, (which from my experience at lvl 60 is around 600-700 mana) cooldown of 10 seconds, and lowers threat by 600 (equivalent to the lvl 50 priest fade). 
 
The priest's fade is a ton more mana efficient, is instant cast, and works for multiple mobs. The druids cat/cower takes about 2 seconds all in all to pull off, costs significantly more mana, works for only 1 melee target, but can be cast every 10 seconds. 
 
If a Priest fades and it fails, hope his PWS will last long enough for someone to pull the mob off him. If a Druid's cat/cower fails, hit dash and kite the mob around the room yelling "ahhh aggro help!" or don't because MT's really hate it when you run and you have aggro, they say run to them (yet when I run to them it seems like all that happens is I die closer to where they are as opposed to farther, silly tanks) Honestly though, most mobs can't catch you running at 150% run speed, but remember during those 10 seconds your party is receiving no heals. Either way, both classes are in a bit of a jam should their aggro reducing abilities fail.