Photo syncing lets you store your mobile photos privately, then choose which ones to share. Right now photo syncing is a test and only available for some people using the newest Facebook for Android app. Facebook Help Center
Seems a bit odd that this is not available in the iPhone app (even as a test), given the level of system integration Facebook is about to get in iOS6. Or could this be a last-minute surprise Apple-style? In any case, not sure I would want to use such a feature, given Facebook’s track record with privacy.
Also sync is such a misleading label here; the app doesn’t sync anything, it just uploads photos to Facebook’s servers.