On the one hand I'm surprised that the church is even allowing Facebook access. On the other hand, the LDS church has always been pretty accepting of technology. And, like it or not, Facebook is a weird phenomenon. It has its fingers in our culture in a way that is hard to ignore.
I think it will be a long time before we see any other social networking stuff being approved for use by missionaries, since every dumb tweet by a missionary will be passed around the internet as official church doctrine. Disallowing that sort of thing saves a lot of headache, I'm sure.