With one in three Americans now classified as "obese" this lawsuit asks a (fat) burning question:

Who is a "Customer of Size"?

Southwest Airline's published policy:

Customers who encroach upon any part of the neighboring seat(s) should proactively book the needed number of seats prior to travel. The armrest is considered to be the definitive boundary between seats and measures 17 inches in width. The purchase of additional seats serves as a notification to Southwest of a special seating need. Most importantly, it ensures that all Customers onboard have access to safe and comfortable seating. You may contact us for a refund of the cost of additional seating after travel, provided the flight does not oversell (which means having more confirmed Customers than seats on the aircraft).

Here is Southwest's Q&A on the issue:  http://www.southwest.com/html/customer-service/faqs.html?topic=extra_seat_policy

A woman of size has now sued the airline: http://www.alltheweigh.com/2012/05/the-law-suit/