Unless you live in the woods, most of the metropolitant areas have Asian Travel Agent who can get you Visa to VN by obtaining a good clear scanned copy of your US Passport information page, a scanned of your Passport size Photo, email to the agent. Done deal! Visa will be issued when you come in and pick up the Ticket or mail to you with your tickets.
Sending passport to the consulate/embassy is "old school"! I am with you on not-trusting ANYONE with my passport. People may question "how can the travel agency be able to 'issue' Visa to you?", no they don't, travel agency apply sign up with the Consulate for pre-approved Visa form, all they need is to match up the ID/Passport with the name, write the name on the PINK visa form, glue the passport photo on it, and there you go, your brand spanking new VISA to VN. $30!
Question I had before, how do they know if people don't make fake Visa to VN? The question here is, what will happen to you if you try to enter VN with a fake Visa?

Thinking of 100 ways VC can make you suffer... for starter, lock you up for a few days/weeks without "1-Phone-Call" to your lawyer/US-Consulate? Then kick you out, banned you forever to return to VN? Or they can say: Visa is invalid, turn around and head home!
So back to the original question, I trust USPS not with all my heart thou! Nobody complains that they lost their passport before, at least on VN-HCMC Board!