Fair warning -- don't sign your posts, profile to the left tells us everything. A reminder to also capitalize I.
I thought about that question too, if i should gem HASTE or get along with INT in the future. I came to the point, that haste is more efficiency.
My gear is almost BiS and i dont have any manaproblems at all with unbuffed haste"cap" (i say cap, cause my greater heal goes in 2sec now unbuffed - 18% without Enlightment in Charscreen/24% unbuffed with Enlightment).
I am almost every time tankhealer (except Twins or Freya3Adds) and it works fine. I like the way to play with Greaterheal much more than the playstyle with Flashheals. I hate the feeling to get 4.5k Flashs on my Tank, who gets immens more damage then i could outheal with FH+Penance+Pw:S. Now i can greater almost all the time, in addition to my penance/Pw:S ofcourse or flash if i have to move.
For example Algalon25: I heal our tanks with a shaman and a paladin on my side and its realy easier to know, that i CAN heal the damagespikes if my mates got to move (cause of blackhole explosion or cosmic smash) without any thoughts about the pre-Shield to get borrowed time up.
Last Algalon i used 1 manapot, my fiend and got tide after 2nd bigbang and left the fight with almost 20% mana left. The efficience of my heals jumped up to rarely 150% of what i healed before (in comparison to the last fights, with same healmates and Int-gemming)
In Addition i can reg much more then before, cause i can afford to heal with more precision and often gain more time to idle in 5second rule.