A friend used one last summer for a 25 day backpacking trip into the Frank Church River of No Return Wilderness area in Idaho. Each night he turned the unit on to broadcast his current position. It was pretty neat to monitor his progress on the internet. You could follow his progress using topo maps or aerial maps.
Before he left he had laid out a specific route. With each day's broadcast, an email message would be sent to the folks tracking his progress. He had a choice of three different messages. 1)"I am OK and sticking to the plan" 2) "Something minor has happened but I am still OK" and 3)"I am in trouble, send help". Message three was never needed.