I don't know about "annoying", but I've had many items (valued from $20 to $8000) arrive safely in Japan from the US via USPS. In fact I prefer USPS to Fedex or UPS, who charge ridiculous "brokerage" fees. I have also sent quite a few items to the US, Europe and Asia by JapanPost without a hitch. USPS tracking is pretty horrible, unfortunately. The site is updated only once a day, and sometimes there are inexplicable delays. It can take 4 or 5 days for a package to travel from San Carlos to San Francisco, and then two days to get to Japan. And once in a while, USPS decides to send my package to Tokyo, rather than Osaka, which is an hour away from Kobe, where I live. JapanPost on the other hand, tracks in real time, in both directions, and customs/transit time within Japan is usually not more than a day.
Customs forms are usually the same everywhere, no? A simple "To", "From", a declaration of what is being sent, and the value, which is all on the same shipping label that goes on the box.
And service at the Post Office is exemplary, so there are no "annoyances"
Cheers,
Kumar