When I joined in late 2011 it was both something and nothing.
Word was you could help 20 people and get 1 point or you could post good stuff and get many but it didn't make you always right.
I was almost to 800 when the forum changed IMO too much and the Karma button went away. Well, it changed to Likes.
So now I've got the Karme > 1000 (or whatever) badge!
The Forum is dead, long live the Forum!
It's a khameleon.
nuff sed...
Tom.. 
I will forever be grateful we got rid of that negative-karma thing. That was truly unpleasant.
awk... word.
Well I am stuck at this value of 2500+ imported from when the forum changed over to likes. In addition I have "badges" that almost double that. But I have asked the moderators and there is no way to add the two values together to give my true value, just one of the other.
In the old days you could add a starting tag line to your posts, but that is not an option anymore.
That is what I found on the old forum. But now some people give a like for everything you post regardless of its usefulness. Is it a new generation of users more used to social media and freely giving a "like" or is it simply the change from Karme to Like?
It’s a different definition of like. It’s no longer “you saved the day and brought light to my issue” anymore.
I use it when something is funny or meaningful in the context or I learnt something or as a sign of encouragement… it’s not purely technical, it’s a pat on the back and the count doesn’t mean what it used to mean in terms of recognizing expertise and support.
How do you use it?
Negative reputation / downvoting seems to be a sport here: https://arduino.stackexchange.com/ . But, in all fairness, that site's purpose is to build up a question/answer database which they don't want cluttered up with "newbie" type issues and which they can later monetize. Helping people is really only a secondary concern.
Precisely as you described!
And also as a means of saying "yes, I agree", or "yes, that's also a way of looking at it; thanks for adding this", or "yes, that's an important nuance that I forgot to include" or "yes, we disagree, but I like how you argued your position and I enjoyed the exchange".
That was before my time... or at least I don't remember it.
I got a badge for giving more Likes than I got!
One feature of many on the old forum I miss was post time stamps where you could see how long replies took, sometimes just seconds apart from each other.
I miss the sarcasm of PaulS... he made me think before I laughed!
You can hoover over the time at the top of a post (left of the post number) which will give you the time of the post (without the seconds).
You're not the only one. But as I understand it, his sarcasm was not appreciated.
I use the like button for posts that are helpful or I agree with.
Yor Mileage May Vary -- he had a certain terse style to it, not mean but coldly accurate.
Some folks make disagreement personal, they missed his hints. He made people reach but provided substance for that effort.
He did not make gratuitous cuts, there was always a point however when challenged that point could be about some lack on the part of the challenger. Hey, they got what they asked for!
Sorry Grumpy, no badge could represent your true value!
I do not believe Arduino would have had the impact across the globe in STEM/Education and the maker community without this forum. If the forum was behind a pay wall, or monetized with fake ad posts or in some other way, and was not as pure as it is, I believe that would be the death knell to Arduino, should they decide to change or do away with it. In that sense, Karma is still a thing.
I like to watch users spin up 100+ comment threads, starting with "give me code," meandering through the kitchen for stone soup, and finally awarding themselves the solution. Seems fair, in today's world. : | (and I like to separate my emoji parts with a space so I don't get that plastic, stylized yellow fellow - sadly, no award for that).
Most of them don’t see it that way. They see the tick box as a way to mark the thread as closed, solved.
When they do that and someone obviously deserves the tick, I sometimes tell them. And sometimes they do it and sometimes not.
However, I never do this when I provided the solution as it looks unseemly.
I normally use this text
Please read
Thanking the people who helped you
And consider if you have done this correctly.
If we all did that then maybe the message would get through.
I understand your point. However, others that find the topic might jump to the solved post that might not reflect the solution.