Pubmed has decided to dip its toes into social activities by adding a commenting feature to it's website (named Pubmed Commons). It will start off in a closed pilot phase where you have to receive an invite in order to be able to comment but it should eventually be widely available. The implementation is simple and everything works as you would expect. Here is a screenshot with an example comment:
As you would expect you get an option to add a comment, to edit or delete previous comments you have made and up-vote other comments. In future versions you will be able to reply to comments in a threaded discussion. The comments, at least for now, cannot be anonymous and in the pilot phase you have to be invited to join. It is also restricted to authors that have at least one abstract on Pubmed already. There are arguments in favour and against anonymity but I lean in favour of identifiable comments to keep the trolls at bay. In this way the comments are also associated to you (via your NCBI profile) and can be listed. Unfortunately NCBI accounts are still not possible to link to an ORCID ID but that should be easily fixed. You will be able to search articles that have comments are these will be made available through their APIs.
I am sure there will be several criticism such as the fact that is invite only or that you are adding comments to articles that you might not even have access too. Overall, I think this is a great development. Commenting systems have, for the most part, failed to work on the publishers side and the hope is that this might finally create a discussion forum with higher participation. The advantages here are a higher visibility and lower friction when compared with most publishers existing commenting systems. For ALMs it might be also very positive assuming this does increase the level of participation. I for one would like to have useful opinion attached to articles while I search for them online.
You can get the whole back-story from this post by Rob Tibshirani and from many of other blog posts and press releases that I am sure will be hitting the web today.