For me I don't like 'like' unless there is also a 'dislike' (seems pointless and ever so slightly dictatorial to only allow people to be positive)!!
But as has been said, that can lead to trouble.
so rather than rating or stamping opinions in a competitive way, I'm a massive fan of a simple 'thanks' button. It's a very simple way of thanking a person for a post, for whatever reason you found it useful or interesting. The key thing is that it allows people to show gratitude without picking sides or casting votes on a potentially controversial thread.
Its also great to display how many times a member has been thanked, as it effectively rewards members for posting thoughtfully, and also helps new members identify how much confidence they should have in responses from existing members (if someone has posted 500 times and been thanked 400 times, it's a safe bet they know about whatever they're posting about).
Lastly, it's just plain good manners to allow people to say thanks, even if they don't have anything specific to say in a follow up post! Just a casual 'thanks'.