How do you tell which posts received +/- karma to know which comments were supported/opposed?
Karma is based on the person, not based on the posts. Thank yous are based on the post and I just readded them after the forum update 
Neg!
Karma/Smite is based on the text written in the post, and you either give Karma if you approve or likes what is being written, that said
if it is of a unique nature. Or you smite it if you are directly of a
hatred nature, not to be misunderstand as
trolling.
The system should not be used based on personal resent towards anyone, regardless of your personal feelings against that person.
And yes the system is purely abusive also, that it can be altered via 1. administrative powers, 2. buddy banking, since there is no direct list of person giving K/S nor is the person giving K/S forced to write a reason for it which is linked to the post that the K/S was given for, present in the current system. So yes the default K/S fails to uphold any whatsoever logic nor has it any valid reasoning in its current system.
The Thanks is, however, is based on the fact that a person was giving a helpful hint, guide or other useful assistance towards another.