The weight and size is phenomenally light. Previously it felt like and was about the size of a brick. The SPOT phone is the size of an older Nokia- not unwieldy at all. The antenna even cleverly collapses and rotates so that it stores flush with the body of the phone, for no excess size. The batteries are also light and small, so carrying spare rechargeable batteries isn't a drag at all.
The coverage of the phone was fantastic. Even surrounded by mountains and trees, it was reliable trying to find a satellite in the sky. Before I may have looked like a crazy person, trying to keep the antenna pointed towards where I thought a satellite may have been. Now, though, I can comfortably sit on the beach, knowing that I don't have to point right at it!
Finally, the call quality - it sounded just like a cell phone. Previously it was scratchy, muted, and cut in and out. I had no complaints from anyone on the other end at all - in fact, people commented on how good it sounded.
It isn't something I can afford to take everyday, but for big expeditions I think that being able to access weather and plan resupplies it is very helpful, and if we had any emergencies it would have been a lifesaver.