As for the RF performance....You have to realize these are very simple, very weak signal FM transmitters in the first place. This means they are purely line-of-sight. With such weak signals, all manufacturers will emphasize the need for a clear window to the sky. Any obstructions or other attenuating means will severely and adversely affect their performance. Anyone who has stood under a substantial tree and tried to use a GPS will understand this.
Also, I've been reading some of the comments here and will say I think you are putting way more faith into these instruments than I am willing. I think that will continue to be the PLB's achilles heel as more people buy up these instruments rather than seek out proper outdoors related training and skillsets. About the time these things started to hit the shelf at REI and other major outdoor retailers, problems began to mount. It's still too early to tell if these problems will sort themselves out as people become more aware of exactly how and when these instruments are meant to be used. Personally, I don't think it would hurt to require simple licensing for the users.
Here is another article I found from a backcountry ski/board site.