Weird thought, but I think that with this license MongoDB has managed to attack the OSI without attacking the FSF. To me, this is perfectly acceptable Free Software but so strict that it basically reads "do not use this software commercially, it requires you to open every piece of software that any of your employees have ever seen or heard of, including software you do not own. Purchase a license from us." In other words, commercial usage is allowed in the post-revolution Free world that Free Software hopes to bring about, where people have access to the contents of the computers that they interact with, and the freedom to mess with the ones they own.
The Open Source concept, however, is not philosophically based; its primary goal is to allow businesses to collaborate on building blocks, but not to prevent them from taking one of those blocks and carving it into something that they're not willing to share. Since their primary goal is to help business, they can't help but disapprove; since they don't explicitly state this goal, they have no nominal basis to reject it without rejecting Free Software in general.
I predict some eventual announcement that the license is "effectively closed source" and instead of accompanying that announcement with a specific supporting argument, they'll accompany it with a questionable written history of the OSI. They'll disapprove, or approve with asterisk.
edit: and, of course, what kemitchell said.