give it a day, it'll probably show up. The 'scan' procedure with USPS is that when the package arrives at the local delivery office, a clerk scans the package to a delivery route. Before the carrier takes the package out for delivery, he/she scans the package to carrier possession. When the package is delivered, it's scanned as delivered.
Chances are good that the package was scanned as delivered when the carrier arrived at your home, but he/she chose NOT to leave it unattended because, a: it wouldn't fit in your box; b: nobody was home to sign for it; c: it was raining and might have been damaged. Was any kind of 'delivery attempt' slip left in your mailbox? This is standard practice for USPS.
The USPS isn't as bad as you guys think. The system is fubared, but the carriers themselves are usually pretty good at what they do.