After reading an interesting related discussion on GenderGap, I have queried the top 10 users of the thanks feature last month, on both the English Wikipedia and Commons. Snapshot image attached and report link below.
I note that the Commons list is heavy with people like myself who nominate, and vote on, featured picture candidates. I have learned there that it is common to thank someone who votes in support of your nomination (nothing wrong with that). I put that practice to good use in thanking everyone who voted for my own recent nomination (https://commons.wikimedia.org/wiki/Commons:Featured_picture_candidates/File:...), and was karmically rewarded with the first-ever featuring of an image I took myself (though I should also really thank another editor who did some late perspective correction on it).
Is it possible to break down the edits that get thanked by namespace, or even a particular page? That would be interesting.
And, overall, I am +1 to the idea that it makes Wikipedia a better place. My only suggested improvement would be a "you're welcome" button, since I receive more thanks than I generally give and that makes me look a little standoffish. (And while we're at that, is there a stat on which editors get thanked the most?)
Daniel Case