Priest can keep the whole group alive, provided each know what they are doing, however in PUG I've bad experience and normally will just keep the MT alive. for others when I see they are not full health I'll just toss a renew on them, here is why;

Mage - they should not draw aggro in the first place, I got a mage too, if Warrior is good there is no reason for you to get hit. anyway If I heal you and the mob will turn to me, and you can't Taunt it off me and I end up used most of my mana to keep me alive... when I went oom and tank die grp wipe... So if mage get aggro L2IceCube/frostnova.

Hunter - Silly hunter like to draw aggro off their pet, they will feint death/ice trap anyway so heal on them is no point, coz if they feint mob on you = WIPE

Warlock - Warlock is the worst to heal... they can't frost nova to slow mob.. they can't feint death.. if they dun get VW/Felguard/succy to draw aggro away from themself, dun expect he will help you when you bashed by mobs.

Rogue - skilled rogue = heal, coz they are good off tanker and need to keep them alive... silly rogue = mana sink, especially when they draw aggro off tank, and most of the time they will vanish and aggro on Healer >"<

Shaman/Druid(non-Bear form)/Pally/Priest - Heal yourself... you are secondary healer in the grp anyway

DPS warrior - dunno what to say about them

However if everyone know what they are doing I can keep the whole grp in 90%+ health with no death toll

So priest can heal more than 2 ppl... they can even keep the grp alive from AOE boss. But if the grp sux, you'll get oom and wipe, then they will blame you

Local WOW news; today a 1000's of Gnomes invaded Orgrimma, did I said Gnomes? I mean Naked Mage Gnomes. Inorder to celebrate "snow ball season", they were throwing ice ball(bolt) to everything insight. Thrall flees from his throne when he sighted these naked gnomes, however local Orc Grunt and Horde Nub had put up meaningless retaliation against the Gnomes Invasion, Orgrimma was cleared in merely 15 minutes, no horde humanoid life spared in this process. This Is Shopboy your friendly News Broadcaster.