Until and unless they fix this, you can get XP for completing an encounter via dialogue, quick save and reload, then kill everyone who was in the dialogue and get XP again. Note that the save/reload is required or you won't get XP for the kills.

It used to be you could KO them for XP, reload, and kill them for a third round of XP, but that was fixed in today's patch. Saving and reloading with KO'd opponents and killing them apparently no longer awards XP again.

But as Gaming Phreak says, if you want max XP, go around and talk to everyone first and do all of their quests. THEN kill them.

Note you'll get to max level LONG before the end-game if you do this. At which point the desire to kill literally everyone may fade. Mobs are only worth as much as their loot at that point, and you may have already have so much loot as to make the killing just not worth it anymore. :P (This is what happened to my husband and I.)

[Linked Image from coloden.com]