As they say in the FAQ's

Does the fee give me access to DIRECTV® for my entire trip?
There is a charge for each flight segment you travel. Once the plane lands and the aircraft door opens, you will have to swipe your credit card and pay again to access the system.

More info here
http://www.continental.com/CMS/en-US...TVWhatsOn.aspx

Remember it only works over the US, so if you are flying outside the 48 you probably won't have it all flight.