A few weeks ago we launched karma notifications, and I've been overall pretty happy with the feature. However, we and many other users noticed that while the current system treats upvotes and downvotes as symmetric, humans tend to definitely not perceive those two as symmetric and so the lived experience of having a single day with a slightly negative karma total tends to outweigh many days of strongly positive karma scores.
I also noticed that this experience has backpropagated into me being much more hesitant to downvote users or even to remove my upvotes since I know they will perceive this as a downvote and if they are not a frequent user might feel quite punished as a response.
As a consequence, we decided to hide negative karma notifications for users by default, though you can change that in your settings. My current model of users suggests it is very unlikely for users to not notice if they are getting significantly downvoted, so I am not very worried about that information getting lost, and I expect it will overall make people's site-experience better (and their beliefs about the value and reception of their content more, not less, accurate)
For some more context, see this discussion on my short-form feed.