The entire narrative behind MongoDB in the first chapters of its evangelism was performance, partly due to its document-oriented approach (things are quicker in some scenarios when you get rid of relations, and it was contrast against the many tables approach), which is something that you can only very recently do in pgsql, and partly due to implementation choices like the dangerous default lack of fsync.
Early evangelism for Mongodb was overwhelmingly one that hyped performance over all others. It was, somewhat infamously now, webscale.
So now pgsql (since 9.2, but vastly improved in 9.3) can also do the things that MongoDB does, better, if you want to do the document approach (which is a serious debate unto itself). That is news and is interesting.
As for scaling out, I would argue that 9.3 offers more realistic, robust options than MongoDB does.
I wonder if Node.js will follow the same fate...get a nice dose of reality check.
It is mistakenly evangelized as also being faster, leaner, scalable, more concurrent than anything out there. Some clients would pay extra to redo CRUD using Node.js because it's "Asynchronous and We wanna Pay For Speed and Scalability".
Wow. That's interesting, I really did not find asynchronous programming easy, with basic things like hooking up to database requiring you to go deeper into a chain of callbacks, forcing you to rely on duct tape solutions like futures or whatever they use now to work around the limits of Javascript, or having to write stuff in Coffeescript.
But some devs swear by it, I just fail to see what the advantages are.
Early evangelism for Mongodb was overwhelmingly one that hyped performance over all others. It was, somewhat infamously now, webscale.
So now pgsql (since 9.2, but vastly improved in 9.3) can also do the things that MongoDB does, better, if you want to do the document approach (which is a serious debate unto itself). That is news and is interesting.
As for scaling out, I would argue that 9.3 offers more realistic, robust options than MongoDB does.