I track like crazy also and when things go "ground" there will sometimes be a delay between cities of several days. But then again I've had mistakes where it got delivered while the tracking was never updated. FED EX Home Delivery is notorious for those long delays. Normal UPS and FED EX are pretty good.
Both FedEx and UPS use intermodal transportation - that is, truck trailers that are also carried by rail. Over long distances, they often put the trailers on a train, and it can be a few days before any change occurs in tracking. For example, I had a package from Canoga camera that left Van Nuys, California on 2/10, and arrived at UPS's hub in Memphis, Tennessee on 2/15.

