I was testing out this expoit with my lock when I noticed that if I use drain soul on a critter (sewer rats and frogs) I get three soul shards. Since critters don't award experience or honor I don't think this is intended. So if you are all out of shards in a boss fight and there is some critter nearby, one souldrain tick = 3 shards.
Also as demo the Decimation talent now triggers if your spell kills the target no matter what % health it was at when the spell hit which makes it proc when you kill critters.