If you don't know yet, it seems that the new iPhone 5s is affected by a very serious m7/gyroscope/compass bug.
Long story short is that almost all units are off by a couple degrees both on compass (users say) and level and so far Apple as well as all other major tech sites are keeping quiet.
This also affects motion controlled games (racing and flying simulators), maps and the panoramic picture mode.
More info here: http://forums.macrumors.com/showthread.php?t=1644439