For those who aren't aware, it says
1. If facebook sues you, and you counterclaim over patents (whether about software or not), you will lose rights under all these patent grants.
So essentially you can't defend yourself.
This is different than the typical apache style patent grant, which instead would say "if you sue me over patents in apache licensed software x, you lose rights to software x" (IE it's limited to software, and limited to the thing you sued over)
2. It terminates if you challenge the validity of any facebook patent in any way. So no shitty software patent busting!
I think React is a great tool, but I didn't realize this license change happened on October 8th, 2014. Prior to that it was Apache 2.0 licensed (which is my license of choice). After that, React is licensed with BSD plus their special patent document (described above). Bummer.