I guess I have been really lucky, I have never had a problem using UPS or USPS. I routinely overpackage though, because you have to assume the worst is going to happen during shipment. Remember, if you tossed packages for 8hrs a day, 5 days a week, it would be human nature to become rather nonchalant about it, especially when you're making about minimum wage pay.
I have shipped guitars to South America before. Now you talk about being WORRIED that it would arrive in safe condition....ship a $5000 guitar 7000 miles!! Double boxed, wrapped in cloth, then bubble wrap, then packing peanuts, then another layer of bubble wrap, then styrofoam, wrapped in cardboard! It arrived safely though