Zeynep Tufekci:

Mr. Grewal is right: This wasn’t a breach in the technical sense. It is something even more troubling: an all-too-natural consequence of Facebook’s business model, which involves having people go to the site for social interaction, only to be quietly subjected to an enormous level of surveillance. The results of that surveillance are used to fuel a sophisticated and opaque system for narrowly targeting advertisements and other wares to Facebook’s users.

It’s a breach of the most basic level of trust, hell all levels of trust.