When Apple launched their MacBook Air's last year, they implemented a new system for measuring battery life. My experience with the 7-hour battery of the 13-inch MacBook Air, is that it does last almost 7 hours in real world use. With other manufactures, you generally get 66%-75% of the published battery in real world use.
The new 2011 MacBook Pro's list a 7-hour battery life as compared to the previous models 10-hour. But the new models apparently have more endurance. LaptopMag just reviewed the 13-inch MacBook Pro and wrote:
Last year when our 13-inch MacBook Pro achieved a very long 7:48 of runtime we were very pleased. Understandably, we were extremely happy when this new MacBook Pro 13-inch persevered for a marathon-like 8:33 on our LAPTOP Battery Test (Web surfing via Wi-Fi).