This would actually put them head to head with Google on the street navigation front. One advantage of Waze is how the routes are dynamically updated by it's own users.
I dread to think what FB will do/attempt to do with the 'Waze experience' and the near-realtime info pinpointing all the users.
(Waze Area Manager and non FB user)
(and in response to the "why all the FB hate" comment: I don't hate FB. I used it rather a lot. However, I try to limit the amount of information FB knows about me as much as reasonably possible. Where I am nearly up-to-the-minute, and not only current and historical location data as well as a decent ability to predict where I'm going on most given days, that's too much information for me to willingly hand over to FB. Or anyone.
Waze knows where I am, but not necessarily who I am. FB knows who I am, but not necessarily where I am.
I don't trust either company with both data sets.
Facebook's long and troubled history with personal privacy, and tendency to combine disparate bits of personal data in ways that some people find invasive.