Please lets keep the discussion nice.
I know there are mixed feelings about a few of these functionalities, "born" from social networks, which may or may not make sense for forums. There are clearly common grounds between social networking and community building software, and there are definitely specific targets and goals too.
This particular one has been requested for ages by our users. I tend to think it has come to the point where expectations of users, shapen up by their experience with many sites over the web (not only social networks, but also blogs and such), are reaching a critical mass or close to reaching it, for forums.
Just to be clear, however: we are extremely unlikely to consider it for SMF 2.1, which has a few new functionalities but it's mainly targeted at
strictly necessary enhancements for 2.0 forums. While we may consider it for SMF 3.0, and please, feel free to add more thoughts and experiences on the matter.
What we should do - and I'll look into doing this - is to make an official mod available to the community on this, kept up to date for SMF 2.0/2.1. It would help knowing better how much interest there really is or continues to be. If you - those doing it already - wish to share yours, please feel free to do so, or point me to it if I missed it. The main requirement is only to be Open Licensed, while we may discuss others.
For the record: I've implemented a "like system" in my SMF fork, just because I thought it was fun to do and to give people something to like. It's a bit like "panem et circenses" in ancient Roman culture - not necessarily a brilliant idea, but it serves at least one purpose: It makes people happy 
That's basically the answer I obtained.
I think this is true. It's not about I don't know what statistics or processing of 'liked' posts, it's mainly about a loose and relaxed wish to click once to express their agreement/interest and be happy they're able to.