For me the hearts are messages to you. I saw it, I liked what I saw, but don't really have anything to add to the conversation. So rather than writing a comment "I like this" I press the like button. Is that not meant for that? Heart, Thumb or whatever it is just a symbol...
Same. I also use it a lot for when someone else commented what I would have written. So instead of writing a redundant reply I just click the heart.
