FSE has been very lucky to have so many healers up to this point.  The class balance seems to swing back and forth and eventually we'll probably have a ton of something else.  I know I have been watching my overhealing % lately and it has grown only because I don't need to pay as much attention with all the manapools available who can pick up the slack.

I think if we're going to be on our game and take another step toward some bosses currently and in the future expansion that will be more challenging the healers (myself included) need to find ways to be more careful about wasted mana on a target that is already topped off.

Some of the things I know have made a huge difference in my own efficiency are using my lower rank healing spells.  My big slow heal as a shaman is a 2.5 second cast with talents and heals for 2 grand + my healing on my gear.  It's my most mana efficient spell.  But it's only my most mana efficient when I don't overheal and that entire 2000+ is being turned into health and not an overheal.  Since it's my slowest cast time, I can interrupt  it if I see my target has only taken 1000 damage or gets another heal before mine.

Since I've been using the same spell but one about 3 or 4 ranks lower (for about 1k healign), I can keep casting it, and since it's my slower heal it's easy to apply the breaks if need be as well.  It saves so much mana and even gold for manapots it's been a huge jump in my ability to heal the raid.

For those fights where I know the tank is taking all the damage and needs constant quick heals, I do use my 1.5 sec cast which I don't get as good of mileage out of, but I even rank it down sometimes because I know that  plenty of 1.5 second heals for 600 are going to be better as far as less overhealing with 5 healers on the guy taking damage and their heals popping like....well stuff that pops alot...like pop.  Or bubblewrap...yeah, that's better.

I don't have any heals over time, so I can't speak to that but I know you that do have strats to get the most out of that spell as well.  

As a shaman, I do have chain heal which is great where the off tanks and melee are taking damage and I still want to heal the main tank some too.  Chain heal does a good job of dropping a little on several targets.  It's also great on a group of locks or casters who are lifetapping or taking some damage in the back for anywhere between 800-200 health per target it hits.

Anyhow, I think we've been doing a good job healers, but I know when I look at the overheal stats we could be at least saving ourselves some money, and extending the survivability of our tanks and other classes.