For the pve shadow priest, there's not much to write home about. We may be able to cast fear ward in shadow form, which will save a bit of mana in a few fear-sensitive encounters. I don't use it enough to care (I assume PVP would be another matter).
One change, however, hints seductively at better times ahead:
Spirit-Based Mana Regeneration: This system has been adjusted so that as your intellect rises, you will regenerate more mana per point of spirit.
Don't ask me how mana regeneration works. It has something to do with spirit and involves all sorts of horrendous, stroke-inducing equations. I don't have the brains to even tackle it. But I do know a buff when I see one. This should hopefully see our two mana regeneration talents, spirit tap and meditation, work a bit harder for us both in and out of battle.
I'm reserving judgement till I see the figures (or, to be honest, till others have seen the figures and told me what they mean). If intellect is to increase mana regeneration, the crucial question is by how much? This could significantly improve our longevity in battle and while grinding. Or, given a shadow priest's notoriously small mana pool, it could see us at the back of the buff queue once again.