My current life is a clonk. 12/2 cleric/monk at the moment.
I've been grouping a lot with another cleric, and aside from a pug where someone is using twists, he and I will almost always be 1 and 2 in the kill counts. That doesn't always tell the whole story though, and often times we'll have a party member doing paralyzing duty which gives others the kill counts. Anyways, the point was to address someone's idea that clerics aren't DPS. Any class can bring good dps, just how they play it.
As to healing, well, there are times I simply don't notice someone's health in time. My own health included. I'm an equal opportunity health ignorer.. Other times one person had drawn most of the aggro and has run away from our healing. If you're gonna take damage, and you want the divines to keep your health bar above zero, you really should stick w/in range and line of sight. Can't count how many times melee toons grab a truck ton of aggro, and the 2 divines are running around trying to find them to keep them alive. At a certain point, I just stop trying.
I've noticed a lot of warforged melee types that I simply can't keep healed. On some quests I've simply told the character to invest in some healing amp, and I'm through following him around spamming all my mana to keep him alive.
Archer types are annoying as well. They somehow manage to grab all the aggro and then run around "kiting" while everyone else tries to follow and "help". Unless you're kiting through firewalls or blade barriers, I've taken to just let you do your kiting and move on.
I've also played with divines who simple refuse to heal anyone but themselves. I always carry potions/scrolls and do as much self healing as I can, but a melee toon is very limited in his healing choices while fighting. Divines do, imo, have a role to help keep the party healed and alive. Those who don't are, imo again, just elitist a**holes. Maybe just a**holes.
Now, not everyone you play with is an 8 year veteran. There's a lot of newer people out there. If you want the game to be successful, those people have to continue to play and spend some $$. Having all the elitist jerkoffs making their playtime unenjoyable won't help keep the game going. Taking a little time to be helpful will pay off in the long run. That goes for all the "I'm streakin" morons whose only concern is maxing their xp/min.