I "like" posts that make me laugh, posts I agree with, posts with valuable information (Jake Bunce probably thinks I'm like-stalking him), posts in which someone has given me information and there's nothing further to say but I wanted to let them know I appreciated it, and posts by people who have spent a lot of time helping me and one "like" won't suffice - so I Like several of their posts just as a kind of payback. And sometime, posts I disagree with but I thought they stated their case well and I could see their point.
I don't think there would be any need to worry about "Like abuse" if people weren't so determined to turn it into a popularity contest with the "most liked" and "sort by likes" and all those other suggested Mods. If it's just between you and the poster, why the hell would anyone else care whether you're being discriminating enough? It's only an issue if you make it one.