I also found Uwe Rueckeshaeuser’s comment very interesting:

In my own “test” the battery in the new 15″ MacBook Pro lasted 8 hrs and 15 minutes using 50% brightness, WiFi on, Bluetooth off and Energy Saver on. I played music most of the time and used the browser, email, office programs and project management software in this time. So, Apple’s claim for 7 hours is not off at all.

Most competing cheaper 15″ laptops would need approx. three batteries to run for 8 hrs and 15 mins. I am on long distance flights often, and I have never seen a single person carrying three batteries / 2 spares around.