
There are forum softwares that allow 'thanks' (some call it 'karma'), and then in a little strip under someones post it will say 'Theemx thanked you for this post' or if you have several people it lists the usernames, and once it gets to a certain point then it just says '37 people thanked you' etc.
Then in each persons profile you can see how many times overall they were thanked for their post, which gives you an idea as to how useful that persons replies tend to be (or how much they are liked, but this isnt really teh case in the places I have seen it used).
Whether THIS forum software allows it, or whether it would require a huge effort to build I have no idea at all, but in the places I have seen it used, it does NOT result in people NOT responding, its an additional thing, or used where people would have just said 'thanks' or as is done in a lot of places here, a quote of the post and 'like' underneath.