I had been meaning to comment on this thread all week, but have been so busy....I grabbed onto the 3 when SPOT asked us to try it out, and have probably used it more than she has, since I had it out west with me in March. Not only have I flown with it, but I have hiked and biked with it as well.
As Louise said, we have been using SPOT since the first ones were handed out at OSH. We got one of those free, but have been paying the annual fees every year since we find it very useful for me to track Louise - it helps to know when she is headed home and I should start dinner!
The 3 has definitely fixed many of the annoyances from the 1 and 2 - the buttons are so much easier and intuitive to use, and far better for fat fingers. your finger no longer covers up the indicator light. Yes, the unit goes to sleep when it hasn't moved for some period of time, then wakes back up when you get going again. This is nice for normal operations, and I see how it might be a concern from a SAR point of view, but a little logic on someone's part should see that if the unit is stationary off-airport for long, there might be a problem...
The smaller intervals are great, but you do pay more for them - the unit is configured for the intervals you want through the PC and internet when you sign up. I suspect you can change it, but am not sure how their subscription will work for this.
Now that we are operating more and more out west, and I am traveling more for my retirement job, I think we'll stay SPOT customers and keep up or subscriptions - it is nice to know where each of us is!
Paul