Florian,
Where I find a big difference from facebook, and use in scientific discussion, is that highly discussed topics float to the top of the feed and repeat, even when you are not directly involved (unlike facebook where you need to interact with a comment first). In addition, the 'like' mechanism acts more like a 'save for later' mechanism as you can search a list of your likes (so I use it to bookmark stuff, rather than necessarily 'liking' it per se). These are both things I find have an advantage when discussing science, and that I sometimes miss when interacting socially on FB.