The Occupy Wall Street example in particular was talking about their use of what they call "the Progressive Stack" to organize meetings. The general idea was this - people want to speak up, but not everyone can talk at the same time, so we need some sort of system for choosing who gets to speak when. First in first out isn't fair enough when you factor in things like minorities or women feeling more inhibited about speaking, so let's let them jump the queue and speak before people who are white and/or male.

It's an idea that sounds just fair enough to be considered, and has the benefit of both having passionate supporters on the left and of having an obvious path to paint opponents as sexist racists that want to silence women and minorities. The left won on this point at the cost of driving off much of their popular support, and the movement has been marginalized since.

The above is my understanding of what happened with this, synthesized over a fair amount of reading and research. It may well be wrong, and the situation may well be more complicated than I described. As far as I understand it, though, it's the major mistake that the movement made - it let itself be co-opted into caring about social justice at the cost of their other goals.

As far as Atheism+ goes, it's an organized group spearheaded by people like Rebecca Watson who are outraged -- outraged -- at the behavior of atheists being insufficiently pro-woman and pro-social justice. Rebecca Watson in particular has a laser-like focus on sexism within the atheist and skeptic community, at the expense of the larger groups' nominal goals. She's responsible for the whole "elevatorgate" debacle, and responded to Richard Dawkins' claim that she was overreacting by going after Dawkins personally with this piece of loveliness. It says it's not a call for a boycott, but it's a call for a boycott ("Nope, I didn’t call for a boycott. I’m relaying the fact that I have no interest in giving this person any more of my money or attention." I read that as "I want to hurt Dawkins personally but realize that I don't have the social capital to carry off leading a boycott, so I'm going to encourage people to boycott Dawkins while saying that I'm not doing so)

I actually haven't done all that much analysis of Atheism+. I pretty much have discarded it as a group of people who have been successfully derailed by people like Rebecca Watson talking about sexism constantly within the atheist and skeptical community, and want to do the same. Just look at the first sentence of their FAQ

Atheism Plus is a term used to designate spaces, persons, and groups dedicated to promoting social justice and countering misogyny, racism, homo/bi/transphobia, ableism and other such bigotry inside and outside of the atheist community.

They are essentially policing the atheist community for compliance with social justice ideas. Their own website is saying the same things I am about them with different wording and connotations.