Thanks for your reply.
I have noted the same thing about USPS and international shipping -- they're the most cost effective.
I'm shipping a guitar to a friend. I noticed that one of the guitar vendors on EBay was shipping to the same country via UPS for about half of what I would be charged via USPS. OF course I was curious, so I asked. His kind reply was that he has negotiated a volume discount with UPS.
Now I wonder if there is some way to get access to wholesale rates for shipping in the same way that U-PIC offers access to wholesale insurance rates. Cutting my shipping costs in half would make a HUGE difference in my profit margin!