We need to fix two problems with Shadow priests. One is that their damage is too low, especially at epic level. The second is that stacking Vampiric Embrace from too many priests probably represents a balance problem. These changes will go live before Nov 13.
Vampiric Embrace -- we need to nerf it, but we don't want it to be terrible for priests in small groups or solo. So we are going to make it 5% healing to your group (not raid) but 25% healing to yourself. Assume the talents that affect it get it up to this level.
Vampiric Touch -- we're adding some of the damage adjustment to this spell, by doubling the coefficient (from 0.2 to 0.4).
Shadowform -- we're adding the rest of the adjustment here. Your Shadow Word: Pain, Devouring Plague and Vampiric Touch do an additional percentage damage equal to your critical strike chance. Basically if your crit is 25%, your SW:P does 25% more damage. This has the side effect of making crit a little more useful for Shadow priests.
Since Affliction locks and other classes with many dots might ask, we think long term that a good thing to look at is making dots crit. We're not sure yet if we'll do this by just making them actually crit or adding more talents that do neat things with your crit rating, but it is definitely something we're looking at.