Hey B, I got one of these this year, so it hasnt seen a ton of service as far as construction is concerned. I for one think it is a great tool. My mom bought it for me, and more so for herself, and it really gives everyone involved peace of mind. Since a majority of my backpacking is a solo endeavor she wanted me to have a better emergency response plan than, "Don't trip". I just turn on the Spot everytime im moving and let it track me, when i get to camp i let it run for a half hour or so so she knows thats my place for the evening and i shut it down till morning. She has a certain amount of fun and reassurance everyday watching my steps. I feel better about being alone and like the idea folks are at home watching me tramp through the woods. It is cool to look over your tracks when you get home as well.
I just put the spot in my top pouch of the pack and it does a good job sending signals, i think there are a number of missed signals but through the day it gets them out just fine. I have never had trouble sending a signal if i have the device in my hand and think it would do fine transmiting in an emergency situation, but there are times it does show limitation... But as noted in some rei reviews, such is the nature of a satellite device.
Its expensive and you have to pay too much for the services in my opinion but especially after having used it for several trips, the peace of mind is worth the dent to the wallet.
And as far as construction i keep it in the little case, you don't do too much with it. Its still like brand new, and i have yet to swap batteries...i dont for see any problems at this point.