Rather then rehashing it, this is what I got in my recent email from Continental:
“On March 17, 2010, we’ll be introducing a new option allowing you to purchase seat assignments for unreserved, Economy Class seats that feature extra legroom. Depending on the type of aircraft and row, seats with extra legroom offer a minimum of seven additional inches of legroom.
You will have the ability to purchase seat assignments when checking in at continental.com or at an airport kiosk during the normal check-in period, beginning 24 hours prior to flight departure. The price of these extra legroom seats will vary depending on a number of factors, including the length of the flight and market.
Consider this choice when you want extra legroom for more comfort on your flight.
We appreciate your business and thank you for choosing Continental.”