I did get a +Karma notification from the bot, from a user this morning or yesterday night, I actually thought the username of the person who gave it was there, but coming on here and seeing this thread reminded me of that notification, I went back to check and discovered for sure, that there was no mention of who the Karma came from, or which of my posts got the +Karma.
I personally have actually thought about this same thing, like op said, being able to see who gave negative or positive Karma, but after thinking about the problem that could cause for some users, and the hate it could possibly ignite, I saw reasons why not making the person who gave negative or positive karma public is a good idea.
But like bitmover have suggested, i support that we should atleast be able to see or know our posts the got the positive or negative Karma, this way, we could re-read such post to see or learn why someone likes or dislikes it, through and depending on what type of karma is given.