---------- Post added 2013-01-09 at 12:19 PM ----------
Okay, the PBE isn't crowded so I was able to test soul generation. I had ~80 by 20 minutes. Siege minions (and probably super minions) always drop a soul. Your scaling starts at 1, and every soul until 50 lowers that by 0.01. So, first soul is 1, second is 0.99, third is 0.98, etc. Once you get 50 souls, every soul after that gives you a flat 0.5. I forgot to look at my stacks at 80, but at 50 I was around ~45 Armor and AP.
Damage outside his ult is mediocre. I don't see him being a good mid laner at all because there are less angles to grab people at. Top lane could work, but he isn't killing anyone alone unless they are dumb or squishy. Lantern grabs souls for you.
Also, one thing that I haven't seen anywhere and deals with his lantern. If you run outside the little range ring after casting it, the lantern disappears and you get the shield. In top lane this will be great, because if you have to back off you can cast lantern behind you and get the shield when running away.