Entrope - I have zero experience shipping equipment but lots of experience shipping documents. UPS 2nd or 3rd day service to a large or medium size city will very often arrive a day earlier than the service requested, sort of a "hidden" discount. Tracking is included in the price (I'm not sure about Priority Mail). It's a good choice for payment, if time is a concern, and may be cost effctive for large dollar transactions. I've had the same experience you did with the timeliness (or lack thereof) of Priority Mail. Express Mail is much better and it is delivered on Saturday for no extra charge, but the rates are not much less than USP or FedEX.
Lugnut - A couple of years ago I read that junk mail is a significant source of revenue for the USPS, supporting the subsidies you refer to. Makes you wonder what would happen to postal rates if junk mail were subjected to a law similar to the "Do not call" law for telemarketers, which I am sure some people with cluttered mailboxes would support. Oh, I agree that Media Mail is a great deal.