There's a big review that I took part in on backpackinglight.com this week as well:

http://www.backpackinglight.com/cgi-bin/backpackinglight/spot_satellite_personal_tracker.html

Bottom line: it is indeed not to be counted on for emergency use; I found it telling that, at the end of the review when the four of us who worked on the review were offered the chance to keep a Spot, none of us wanted it.

There are some people who are fine with its limitations, and those seem mainly to be folks who want a way to let friends and family know they're OK on a trip, but where the message not getting through won't be a problem. It will work better in open areas with no trees and no significant blockage from terrain, and if it's mounted on top of your pack (not in a pocket or on a belt).