I forsee negligible diferece in healing from my current spec (respeced last week out of boredom) and I only have 11 points in holy, and healed just as well.  Current spec:
http://www.worldofwarcraft.com/info/classes/bc-priest/talents.html?055220013050510000000230051000000000000000050230010000000000000

I'm considering the following spec for BC at the moment:
http://www.worldofwarcraft.com/info/classes/bc-priest/talents.html?051200000000000000000200000000000000000000503250010250123051051
FSE raids, and I think that this spec gives a full prospective of the new talents, and would be most beneficial for raids (other than a pure healing spec), based on the mana efficiency, and benefits that it gives to the raid as a whole.

I would definitely start all fights in shadow form, but will not hesitate to jump out and heal. I'm one of the best off healers around (ask any group that I played the DPS role)