over healing :)  
personally i think there is some unnecessary over concern on overhealing.  I for one use pray of healing a lot.  it is one of my best heals, and most mana effecient.  The only bad thing about all the meters that measure overhealing is that it will show overheal on some people when casting pray on the party because 4 people are at 50%, and one is at 100%, like a someone who just got a heal from someone else.  so by casting prayer, I bring four people up to full health, but overhealed the 5th by 2000hp or what ever the level of prayer i cast.  

The mana difference for some spells is so low, that it is of little consequences to cast a higher level.  for example heal 1 v. 2. or heal 4 v. greater heal 2.  

I have the addon &quot; smartheal&quot; from the curse-gaming.com sight and it lets me know who else is healing my target, and with what spell.  This is great when managing mana.  the only bad thing is when you have to decide to abort your greater heal 4 when you see someone is casting a flash heal on the tank, and the tank is at 50%.  my greater heal will bring him back to 100%, and depending on the flash heal cast give him 600-to 2000health, depending on the casters gear, rank of spell and crit.  in this case i would probably let my GH go off, as it is on a tank, and depending on the boss being killed, as many bosses can crap out enough damage in that 1.5 seconds it would take me to stop and cast a flash heal too.  

I think one of the best ways for us to conserve our mana is to make sure we have people in the groups they are to heal.  for example i often get told to heal so and so who is in group 1, while im in group 3.  this is fine if you don't ever want me to use one of my most mana effecient spells, prayer of healing.  ot me it doesnt make since to have two preists in one group and have them both healing guys in other groups.  I realize that we set teh groups sometimes for taking advantage of shaman totems and such, but if we really focused on the healers when settign groups, we could maximize our mana, spells.  Also by assigning who our primary responsibilites are to heal we wouldnt be walking over each others heals.  by this i mean when we have 6 people who heal, 4 preist and 2 shaman, and we are clearing trash, we often all pop off heals on teh first person who is down in hp.  I have seen the message before that tells me 5 or 6 people are casting a heal on them.  I too will often not bother to stop the heal as it is unnecessary to stop as mana is not a concern.  

so in short, i think that we do a pretty good job of managing our mana.  Sure we cna improve upon it, but just because we (me a lot) are &quot;overhealing&quot; it doesn't really mean we are runnin glow on mana, or unable to heal people.   

plus a lotof healing can be eliminated by people controlling their agro.  I know when the tank able to hold agro, several of us healers are casting dps instead of healing, as it is unnecessary.