But what's the idea in that? People work out of coffee shops because they need a social place with other human beings around. Almost everyone has an internet at home, so they could always work form home rather than being cooped up in a car waiting for the cops to come around asking.
Some are just stuck because they can't go elsewhere because of traffic jams and they don't want to go inside because it's too crowded or too many people waiting in line for coffee (or to go to bathroom).
Afraid I've never heard of anyone being accosted by officers about hanging out in the parking lot inside their car w/ their computer. Who is to say who's wifi they are using anyway (especially in a tight area where you have multiple choices for wifi)?