I used a Spot 2 in October for a 2 week Tunisia trip.
The tracking function worked exceptionally well down through France, throughout Tunisa (including several days 'off piste' between Douz and Ksar Ghilane) and all the way home and never missed a beat.
All the messages I sent were received, I even sent an 'OK' message from the ferry, mid-med. You can even update your facebook page with it if you so desire.
The folks at home were very impressed and some people were tracking us 'live' during the day.
They probably knew where we were better than we did!
We will us it again in Morocco next year.
As I have said in another thread it's an excellent tool to keep the folks at home entertained/informed and a reasonable safety device (if used properly) in a safe-ish contry (e.g. Morocco or Tunisia).
For somewhere further from the beaten track I would go for some additional emergency cover, such as a sat phone.
In summary, be aware of its limitations and its a great bit of kit