I average sending between 2 and 5 items a week to USA and Canada and have never (touch wood) had a package go missing. I send by regular air mail but also print out the PayPal packing slip which shows buyers address and get the post office to stamp it as verification of the address it was sent to. I have no idea whether this would be at all effective or useful in the event of an 'item not received' dispute - luckily I haven't needed to test it yet.

Judging by my two new red dots - maybe American buyers are less willing to communicate when there is a problem and that's something you might need to think about...