I foresee the day when devices will be "better" tracked anyway, good bad or indifferent. But steelmaverick brings up a good point... another reason why a one-way GPS method might be the better way to go.

I'm seriously thinking about forming a campaign around this... just gotta think about it first. We could pick one retailer first (like Starbucks, a good choice actually) and encourage them to use the GPX standard with their location data (see link in my post above). Thoughts?