For every negative story about someone's data on Facebook there are hundreds of people who post stuff on their pages. (you just have to be sensible)
I don't think Mark Zuckerberg is in it for the money, you only have to see his frugal lifestyle at the beginning.
I think he just "likes" the idea of running a big company.
And where else can you get a page up on the web in minutes and start getting hits or likes ?