PubMed has been quite active recently - in surprisingly innovative ways. A few months ago they launched PubMed Commons, allowing comments on citations in PubMed. Recently, they have also added social media - sharing buttons, allowing you to tweet, like, and +1 directly from the PubMed page.
Overall, the grand vision is to encourage a platform for scientific discourse and post-publication peer review. Check out their blog - the posts are infrequent, but they summarize the strategy. There are other websites (PubPeer is a notable one, but also F1000, and the new kid on the block, Winnower), but PubMed is the 500 pound gorilla in this space.
The latest step is the launch of Journal Clubs on PubMed Commons. And guess what, #NephJC was one of three journal clubs to be part of the launch cohort! Check out the press release, and the NephJC home on PubMed Journal Clubs. This is an exciting development - and we are sure more journal clubs will eventually be added, but we got bragging rights for this one!