The long-winded title should pretty much get the question across. There are a few lunch spots here in Boston at which some people throw a coat over a chair to "reserve" a table, while they wait in line to order their food. I have also seen others take said coats and deposit them on the floor or elsewhere in order to "unsave" the table. I have further observed (on rare occasions) fisticuffs almost resorted to to settle the question of title to the seating.
I feel it's wrong, and it should be a first come, first seated system. I plan to "Ask the Imam" at some point, but was curious what others thought of the propriety of this reservation method.