It sounds like the accuracy will be improving with the retirement of some of the older frequencies:

http://www.noaanews.noaa.gov/stories2008/20081031_sarsat.html

The accuracy, of course, depends a lot on where the thing is triggered, with a canyon probably being the worst possible scenario. I would definitely get one with the added GPS function. I understand that EPIRBs cause far more false alarms than PLBs, since they are designed to self-trigger. I'm interested in a PLB since I solo a good deal, but am waiting for a nice four-ouncer!
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--Rick