Wow - thanks guys for all the feedback.
There's quite good reviews of the SPOT device on:
SPOT Satellite Messenger FIRST LOOK - EQUIPPED TO SURVIVE (tm)
SPOT Satellite Messenger Personal Tracker Review (GPSmagazine.com)
One major concern has to be the fact this it's unclear when you send a 9-1-1 message that anyone has actually received it! Bit like transmitting a mayday on 121.5 & getting no response - you'd assume no-one heard, right?
All you get apparently is a bunch of flashing lights, much like any other transmission. Shame that - is it related to this "simplex" vs "duplex" network they use I wonder??