This might be a minor for rest of community but it bothers me quite a bit personally. There is a heart icon representing "like" or agreement with the post. I think that choice of icon is not great as heart implies love, much stronger emotion than simple like or expression of agreement with what has been said. I often shy from pressing the button in situations where I would want to do it, because I feel like I need to be more invested in it to use "heart" button. If it was changed to something less powerful than representation of love, I would probably use it more often. (I might be only one who feels this way tho :) )
Also, heart icon could be mistaken for favourite button instead of like button by some people, reducing its utility even further
Probably any kind of rating system has some issues:
For me, for example, the button does not imply agreement, but rather "I think this post is worth reading" (even people with different opinions can have good arguments ;-)
Quite often, there's just a very specific part of a post which I agree to, and sometimes, I completely disagree with the rest ;-), so I'd appreciate some granularity.
As for the icon:
I guess the heart has no copyright issues that other symbols might have ;-)
I don't use any of those services, maybe that's why it's throwing me off. Now that I think of it, I don't think I use anything else other than this forum that is using heart icon. Well, looks like it quite standard after all, so I guess I will have to adapt
A +1 button would have this meaning, but I disagree that this is what the heart button represents. I currently use the heart button when I think a post is especially constructive, or adding something new to the conversation, whether I agree with it or not. The heart is an effective icon for this, because it indicates ‘liking’ the post without indicating ‘agreement’.
The ‘Summarise this topic’ feature which is enabled for longer threads seems to favour posts with many hearts, so this seems the intended usage to me.