Todd, I had a similar problem a couple years ago.
My incoming was disappearing, my outgoing was disppearing... I complained to the local postmaster... and before I knew it, the next thing to disappear was my mail carrier . Only one package has disappeared since.... last fall, a package from Archie became MIA - never has arrived.

I am NOT accusing the post office... I am a former postal worker and I think the majority of carriers are very honest and dedicated to trying to get the job done.

But - what was strange in my case was, my carrier was a guy that I was hired with back in 1984 (although we didn't really know each other... ). We used to chat about the old GMF (General Mail Facility) and one afternoon, he was having me sign for a registered package. He asked me curiously, "What is in all those little packets you get?" So I showed him... stupid me. It was right after that, I had mail tampering. Sometimes packages would be cleanly sliced open on one end... with no "stamp" or baggie saying it was damaged or found empty (which IS standard procedure).

After MAJOR complaints (via phone and in writing... ALWAYS back your complaints up in writing) - one day I noticed my "old buddy" hadn't shown up for some time. I casually asked the new carrier, "What happened to the other guy?"
She just said, "I don't think he works for us anymore."

I can't say this is happening to you... but I don't mail ANYTHING from my house... I drop EVERYTHING off AT the post office.
I haven't had any missing incoming for awhile(except Archie's package... which was a bummer... it was a neat Harrah's commerative item that may not ever come my way again ) so... not sure if this helps... but it is what happened to me.

Call your Postmaster and write a letter.
I insured almost EVERYTHING for quite some time.
I used delivery confrmation as well. It seemed that "tracked" items had a better chance of getting through - since a point of liabilty can be determined. Will cost you more money... but it may reduce your disappearing shipments.

Good luck!