My girlfriend is doing a research on how data management programs influence on the actual work getting done. Because the data defines the efficiency of the worker, the workers start to do tasks that give them more "efficiency points" - no matter if these tasks are the most important ones or not. And some important task are neglected, because the program doesn't value them (ie. "invisible work").

Just saying, that while this Karma exits, it can't be neclected. It will have an influence on peoples behavior. It's purpose just has to be clear: to indicate the activity (and usefulness) of the member to the community. If giving thanks to someone can be considered as a meaningful activity and therefore something we want to substain, then it should be rewarded with karma. But the amount oh the karma should be in pair with the importance and effort.

But I agree with qgil: the importance of Karma should not be emphasized - you should not start doing things that give you karma, you should be doing useful things and GET Karma. IMHO the amount of thanks on the site is now quite good (they are given, but not for every post), and giving thanks should remain sincere: "I thank you for writing this" and not "I thank myself for reading this".