A lot of your questions can be answered via

Doug Ritter's PLB FAQ: http://www.equipped.org/faq_plb/default.asp

and his "How PLB's work page": http://www.equipped.org/406_beacon_test_background.htm#How

The coverage in Florida is as good as anywhere.

The GEO satellites orbit around the Earth's equator and will provide a very quick response to a PLB beacon - within 3-5 minutes. That will tell the system that you are in trouble, but won't tell them where you are.

Your location is determined - and transmitted to the GEO satellites - by one of two systems:

1. GPS location - a GPS fix gives you a location accuracy within 100 meters, but they rely heavily on a clear view to the sky - especially older GPS chip sets - I have not heard whether newer PLB's use the new high-sensitivity chip sets. If you turn on the PLB with onboard GPS, do everything you can to provide a clear view to the sky including as much of the horizon as you can. In Doug's testing a GPS fix can take anywhere from 1-16 minutes.

2. Doppler location - a Doppler-shift location is determined independent of a GPS using LEO satellites, and provides roughly a 2.5 Km (1.5 mile) location accuracy within 1.5 hours. The delay is less as you move away from the Equator - Doug says the maximum delay in the continental U.S. is about one hour.

The other things to keep in mind:

1. Rescue won't come immediately. It takes some time for them to confirm the validity of the beacon and to launch the rescue. Be prepared to wait for rescue to arrive.

2. At least from what I've read - not all SAR have the capability to take advantage of the 121.5 MHz homing beacon. YOUR job once you've initiated the PLB's signal is to be as "findable" as possible. A while back there was the story of a climber who had to use his PLB for rescue while perched on the side of a mountain. He watched in frustration as rescue teams looked for him off in the distance, but couldn't get their attention - somehow they had the incorrectly estimated his location. Eventually he was able to get their attention. I'm trying to remember how - maybe by waving a space blanket??

3. Don't be surprised if you are charged for the cost of rescue. But then again, what is your life worth?

Don't wait too long to buy one. As you say, a better one will come along next month. Its the same way with cell phones and digital cameras. It used to be that way with GPS's, but I'm not so sure anymore ... they have yet to improve on my wonderful Garmin GPSMAP 60CSx. They've added new models with attractive features but have yet to make a better GPS.