This is optional. I can see how some people would find this interesting. I already do this with Google+, primarily as a form of backup (in addition to Photostream, which doesn't work over 3G).
As far as privacy goes, while Facebook has a history of pushing people towards sharing, I know of no real safety breaches, and their infrastructure is robust. I see the concerns, but for people who share most of their mobile photos anyway, I can see the convenience factor of organizing it in a online, private me-only library. As most Facebook concerns, as long as you are aware of what you're doing you're fine.