Let's be honest. This is isn't the first rumor and it won't be the last. But the rumors are getting louder, and that usually means something. I totally can't blame them for cashing in, when the offer is good enough.
Personally I oppose Facebook very strongly, for the following main reasons.
Yes, driving around with Waze on isn't private at all. But Waze you can turn of or - even easier - not turn on. Facebook has a strategy of getting their nifty little fingers behind everything you do in life. They urge other companies to use FB login. Take for instance all those sites where you can vote for anything, whether it'd be best app, human rights and environment issues or politics, many allow FB-login. Or sites where you can win something, often FB-login. Oh so convenient, you have to remember less passwords. Many companies shift their focus from their own website to their page on FB, their promotions or events are often on FB. And then there's the like and share buttons on all those other sites, that track your every move on internet if you just forget to log off your session with FB.
So yes, there is a great privacy difference between FB and Waze. And imagine what happens if they merge and FB not only knows your internet whereabouts, but also your real life whereabouts. Their advertising will get even more invasive, ads from the pizza restaurant you pass often, ads from the gym if you haven't been to the woods for jogging for two weeks, ads for the cookies you like on the screen of the friend you're navigating to.
My motivation to contribute to Waze is based on two pillars: 1) building a local community in my country so we all can save time in traffic and gas, know about danger on the way and prevent getting speeding tickets and 2) helping build up a sympathetic little start up that once had a brilliant idea come to life. Both pillars can be described as doing something good for the world, helping each other out, building a community that benefits all. My motivation is intrinsic.
That second pillar will be totally gone when Facebook takes over. I'm not spending my free time not getting paid to make Mark Suckerberg and a multi-billion company even richer. Working for Waze hasn't always been satisfying, but in the end you always knew they were doing their best with limited resources. That sense of generously helping grow something small and helpless will be gone.
3) future development
What will happen when a big company takes over a small one? History has shown that often the new big owner totally misunderstands the basis of the company it takes over. Often they die a slow and painly death because of that. Many times they are bought to be put to death deliberately before they become a threat.
And if they keep Waze alive, what direction will it go? How will the app change? Will the map editor stay?
In the end I will probably keep using the app on my phone, unless it changes to much in a direction I don't like. I still like driving around traffic after all. But my other activities will probably be reduced to a minimum, maybe except for the local community things.