If you're not a Protector or a Warrior, and you see me, your friendly neighbourhood divine priest, being hit by a crapload of mobs - DO NOT AOE. (Unless, of course, you can kill all the mobs in that one AoE. Then go right ahead.)
And more importantly, DO NOT PULL THE MOBS OFF ME.
Because you'll die faster than I will if you do that.
See, PWE's game engines have retargetting lag on heals. After I target someone, I need to make sure I've selected them for at least 0.5s (or it could be 1s, I count by 3 spins of my mousewheel upon target change), or else the heal goes to ME. Not my target.
When a crapload of things are hitting on me, I'll be spamming heals on MYSELF, and probably the tank.
If a nice DPS (mages especially, you're so squishy), comes in and says I WILL SAVE J00 I WILL TAKE THEM!!!!!
That DPS will usually die. Not because I'm being mean but because I've been totally focused on, 'Oh oh oh oh stayin' aliiiiiiiiiiiiive!' that by the time I realise what you've done, and retargetted, and waited for the retarget to take... you'll probably be dead. This especially tends to happen in Arena of Souls.
Divine priests are very durable. Especially those with Iron Bone pets.
If you wanna tell the tank the healer's being eaten though, that's great - because I'm usually too busy BeeGeeing to be able to type that. And if you have a spare heal, no matter how puny, healing me with it is sweet. ;)
P.S.: This advice is good till level 49 - my priest isn't 50 yet. And so far trash in FW doesn't have the kind of disabling power that mobs in Guild Wars do, nor do they yet hit as hard as WoW heroics - where you really don't want them whaling on your healer.