So I'm really digging holy now, thanks to the advice from Teacake. Mana management is no longer an issue whatsoever, and the numbers I can pump out really make me happy. I did my first 25 man (Sarth with no drakes, but we all have to start somewhere!) since BC, and it was a blast! My overheal percentage was not all that great, but considering most of it was from PoM, and I can't control where my PoM jumps, overall I think I did pretty well.
I really like GS too, although I wonder how tanks feels about it. Usually, I use it when my group takes an unexpected wave of heavy AoE. I'll throw GS on the tank and work on getting the rest of the group up, knowing that even if the tank "dies", they'll get a massive heal when it procs.
I still feel guilty every time I use it. Does the tank not notice, and think why the heck is this healer letting me die? I assume it's a bit different in raid situations, but still.