I'm at the moment reforging out of spirit I tend to have more mana then the other healers in my 10 man group though I think I am getting close to the minimum.
1823 spirit unbuffed
2493 combat regen with Tsunami stacks and about 3k raid buffed ish
unbuffed
11% haste
11% mastery
22% crit
I'm on tank healing but I tend to raid heal a lot yet mana is only an issue when learning a fight once everyone knows what they are doing mana isn't a problem. I plan to drop a bit more spirit get it down to about 2400 fully buffed.