The thing I hate most about having a PO Box is that they sell your info to everybody. You get spammed at your box AND at the address which was on the ID you supplied to open the PO Box. Also, and I'm not sure if this is universal, but at my local PO, I can request to find out the owner of any given box and they'll share that info with me for a couple of $$.

A PO Box is NOT the way to go if you want some level of privacy.