All healing talents in BC are multiapplicative and also include +healing effects.

Example:

Renew rank10: base healing 970
With +1000 healing: 1970
Imp renew (15%) : 2265
Spiritual Healing (10%) : 2492

Same thing goes with Flash Heal and Greater Heal (Empowered Healing). Pretty confident that these changes correspond to the equivalent talents of Druid/Shaman/Paladin.

According to laz at the Elitist Jerks forum:
Finally, talents like Improved Renew will scale with equipment. This makes a lot of holy talents much more powerful than they were before. This is especially good, since people will be walking around with a lot more health in BC and will need a lot more healing.

Vampiric Touch and Vampiric Embrace can both be active on a target per priest.
Misery and Shadow Weaving seem to stack although i have to test some more on this so take it with a pinch of salt.
As said earlier, mini-shield wall is dispellable.

According to laz at the Elitist Jerks forum:
Finally, talents like Improved Renew will scale with equipment. This makes a lot of holy talents much more powerful than they were before. This is especially good, since people will be walking around with a lot more health in BC and will need a lot more healing.