My take on all this is Facebook's legal team seems to be sending a message to the open source community that they should come for the ideas, but wait for a truly open source alternative to come out before using those ideas in their own products.
I'm obviously not condoning patent infringement. The idea is to learn from useful ideas and implement a non-infringing equivalent as an open source project. You can't patent "math", or "computer science", or ideas comparably broad.
