Having worked as a package handler for UPS for two years I personally only ship things that i know won't/ don't care if break. In the moderate volume hub (~20-25,000 packages per shift) I worked at we would load close to a thousand packages per person a day. While there were people that followed the rules 90% of my coworkers could have cared less if it were beer or anything breakable in those boxes. While ideally they're not supposed to, boxes fall from rollers, get jammed on conveyor belts, and thrown or dropped.
I guess moral of the story, I don't ship breakable things ever. Hell, last time I shipped an aluminum exhaust pipe I wrapped it in multiple layers of bubble wrap because of some of the stuff I've seen. I do like the PET bottle idea though...