From what I’ve read around the internet, 3.0.2 prot and ret paladins should now be stacking strength. You gain spellpower from attack power (AP). You gain AP from strength.  If talented (Divine Strength, 5 talent points = +15% strength), you gain 2.3 attack power from every point of strength.  Ret pally’s should have been stacking strength from prior to the patch, at least that’s what I was doing.

Holy paladins should still be stacking spellpower, but protection and retribution paladins should be stacking strength.