In my opinion, integrating with social networking sites is a terrible idea. It is not sufficient to simply make a set of tags for science commentary to work, you need an active community, with voting, moderating, ensured openness, and good visibility for the highest quality comments. Just aggregating internet comments is not enough, there is no place, other than mathoverflow, where high quality comments on technical papers are positively selected for.
The social media is usually nonsense fluff comments of zero scientific value. You want real biting review, refereeing review, with technical meat, and you won't find that anywhere in physics, mathoverflow is an exception. Besides, the existing social networks aren't worth a dime.
But to answer the question, if someone wants to link their post somewhere else, facebook or twitter, or something like that, that's a good feature perhaps, you can make it easy to do so, although I don't see that as a high priority on the "to do" list.