One of the things we get told frequently is that we need to "expand our social media presence", i.e. to get LinkedIn and academia.edu. This is essentially highly functioning hypocrasy in my opinion, because the same people who advocate it or "follow" your profile, if met directly, do not give a shit about what you are working on.
I have enough of the "so...what are you working on?" question that immediately follows the exchange of names. It is almost always followed by the shortest possible description, because, really, nobody gives a shit. Often enough, even the general topic area is enough to make other people glaze over and switch off. Academia.edu etc. pretend that there is great interest where there is none, and at the same time further the already backstabby and highly disingenious environment within academia.
At least, that's my take on it.
[edit]: It also furthers the already widespread plague of inflating your CV with absolutely bloody everything you've ever done. Given a 15-minute talk as an introduction to a class or seminar? That's a "talk" now, apparently. Organised a club that met (perhaps once) to discuss the importance of petting animals during the exam period, and that asks for access to petting animals for everybody[1]. Onto your profile it goes. Wrote an "article" for the "journal" you and those other people you know "published", made up of your and your friends' articles? Publications! etc.
[1]: I wish I were kidding. I am not. However, since posting a citation for this would reveal a bit more about me than I care to share here, I won't. Take it or leave it!
I hadn't looked at Academia.edu through this lens before. I think it's in a position to accomplish a lot more, so here's hoping they focus on 'impact' and not just 'engagement'.
Kinda like academic publishing, right? Pretty sure the Erdos number[1] was around well before Academia.edu.
To make it clear - I think a lot of Academia.edu's practices are annoying - login wall for papers etc. But academia would be well served if it took better advantage of some of the possibilities online collaboration brought (think of the Polymath projects). CiteULike/arxiv cannot be the high point of online academic publishing.
This has partly to do with the dreadful "tooling" in many cases, i.e. in most cases Word with handwritten citations. If you are lucky, people use Endnote or Zotero. If you are really lucky, you might encounter somebody who knows what (Open|Libre) Office is. Your options for collaborations are thus: Google Docs (if people can manage the technical complexity) or mailing around Word files.