Wow. I've seen voice mail hell before, but the USPS has lowered the pit even further. Their web site claims there's customer service on their 'track and deliver', but I couldn't penetrate the hellwall there.
How to Bypass Most Phone Menus and Get to a Live Operator pointed me to a solution that works, though they close at 8pm ET: "USPS 800-275-8777 dial 7-3-2-0-0".
Amazon claims the USPS delivered a package, but we don't have it.
Update: Amazon took care of the matter.
Update 1/26/07: The "bypass phone menus" site has since now become a business. A great resource.