This is an interesting thread, one that's prompted me to talk to Eric and some local Michigan chippers about possibly going in on 500 Saf-T-mailers (thanks for the pointer, Archie). I agree that for more security, I would want to use the standard bubble mailer plus either delivery confirmation (or more likely, signature delivery, if it's that big a risk). So I did a quick comparison of the total shipping costs for a single, standard chip that makes the mailers look like the best option in most cases. Sorry if I'm just repeating the obvious.

#000 bubble mailer: .22¢ (per in 50 pack)
Postage: $1.13 (DC optional .75¢, but the envelope needs to be 3/4" thick; extra padding might bring weight up)

Total: $1.35

Saf-T-mailer: .22¢ (per in 100 pack)
Flip: .05¢ (per in 100 pack)
Standard envelope: .01¢ (or less, in box)
Postage: .41¢

Total: $.69

The only drawback to the saf-t-mailer is that you can't get delivery confirmation without paying through the nose.

The only question is, would the post office still accept the Saf-T-mailer? John's last response indicates they will, though he also mentioned a .58¢ charge that I wasn't what it would be for.