Is Academia.edu useful? I received a mail today from Academia.edu (a site I wasn't previously aware of), asking me to confirm that I co-authored a paper with a colleague.

Having looked into it a little it sounds like it might be a useful site - the idea of a "social network for scientists" is one I've seen the need for in the past. However, partly due to bad experiences with the seemingly similar ResearchGate, I'm also skeptical.* Without signing up for an academia.edu account the site doesn't offer much information, so I would like the following information:


What specific features does academia.edu offer to its users?
Is it genuinely useful for any of the following purposes (each of which seems genuinely needed)


as a platform for networking with academics
for discovering relevant research
as an effective system for post-publication peer review
for organising references among a small team of people working on a project

Will it send out mails to my colleagues without my express and explicit permission? (I.e. are the mails I received today the result of a deliberate action by my colleague, who is aware that I will be emailed and wishes me to join the site; or are they essentially spam from a social networking site aggressively trying to expand its user base?)
It's clear from its Wikipedia page that it's a private, venture-capital funded company. What is its business model?


In short, is this a site that has some genuine utility for academics, or should I just ignore it?

*I've never signed up for ResearchGate but I regularly receive spam from it purporting to be from my colleagues, who aren't aware that it's being sent on their behalf. I would be mortified if my senior colleagues received such mails claiming to be from me, so I won't touch it with a barge pole.
I distrust it for an entirely different reason. I once wanted to download a paper, and could only do it if I signed up. I signed up by logging on with my facebook account... Well, academia.edu took my profile information, and, without me knowing it, created an academia profile. With my picture, publications it could find via search engines, and a list of interests that were half right and half ridiculous. I'm a neuroscientist; it listed me as being interested in marketing, among other things. I only discovered this profile about a month later. 

Apart from it being entirely unprofessional, I simply do not trust information that is on there, as I have first-hand experience that information on me was wrong.