After many conversations with the techs, I've concluded that most don't know how this unit works; specifically, they don't know the algorithms the unit/satellite/groundstation uses to decide if a message is valid (e.g., inconsistent GPS reading over several send tries).
The "techs" don't accompany you on your adventures. They're not there.
You don't have to know how the algorithms work, either. What you do have to do, is allow the gadget to do its job.
The Spot is a low-power portable GPS satellite receiver, as well as a low-power portable satellite phone. You have to understand that you can't see the satellites, but the gadget communicates in line-of-sight. Even then, any kind of radio echo will interfere with its channels. So when you press the button, naturally you shouldn't stand under a tree, and if you're anywhere near some mountain's rock walls, it will see interference.
Mine also fails when it's too close to my GPS. So if I turn them both on, I'll lay the Spot on one rock, and the GPS on another rock, somewhere else.
Don't forget to review the user instructions once in a while.
Even so, you'll still miss some calls. But that's a hell of a lot better than cell service -- the cell network doesn't reach anywhere near where I travel.