The funny thing to me is that lately I've been leveling a priest as an A/A Disco priest (aka Atonement priest). If the tank is using a proper spec and the dps aren't stupid (purposely pulling off the tank by attacking the wrong thing for instance), then really I can keep my dps to about 2/3 of a dps spec (or more if the tank is well into the habits of using survivability abilities to the point he doesn't need me at all) and have even beat out some lower geared dps.

I have been called an idiot for this, (which was amusing to me because if I don't have to heal the tank, why is the tank complaining about me not healing him?), but I find it highly enjoyable and not your boring stand still and heal occasionally thing. Besides, if I do have to heal, then I'm already able to do it without running out of mana.

tl;dr - why is anyone trying to heal or tank without being speced for it? These specs are easy to level in as well and dual spec is now cheap and easy. If you don't have 10g by lvl 30, I'll give it to you, you know?