I recently had USPS packages lost. You first have to sign up on their website, which is irritating enough. After a lengthy claims-reporting procedure, it was LITERALLY impossible for me to file a claim on their website, as the mechanism was completely broken, preventing me from submitting. When I called the tech support number listed on their web site to report this, I got an advertisement/marketing survey asking me my age (and if you're not in the correct age range, they just hang up on you). Beautiful. Then I called a general help number, selected the "claims / lost package" section, and still wasn't able to talk to a human being (apparently, you could only look up an existing claim by ID). All other options resulted in the same thing. No way to talk to a person that I could discover. I had already wasted several hours by this time, and the package wasn't valuable enough to pursue things further, so I just wrote it off as a bad experience.
NEVER, EVER send anything you deem valuable or important via USPS unless you have no alternative, or are willing to write it off if it goes missing. Most of the time it gets their fine, but if not, you're probably screwed, and they apparently don't give a crap about fixing mistakes like these.
Lost packages happen - I'm not asking for perfection. But I've dealt with other carriers and have gotten rare mistakes quickly resolved.