Apple's Watch is designed to be both fashionable and functional.
Standardized Battery Test Results for the MacBook Air
They setup 3 tasks of varying intensity with the MacBook Air's display set at just above 50% brightness, and not to go to sleep, though the hard drive was allowed to spin down if able. The tasks and battery life times are listed as follows:
1) Use Wifi to browse 20 pages in a loop, spending 20 seconds on each page, while playing MP3s in iTunes. 4hr 16min
2) Play a DVD image (off the internal hard drive) in a loop. 3hr 25min
3) Download 10GB of files, Web browsing loop from #1, play two 480p Xvid videos in a loop. 2hr 25min
As expected, the battery time varies greatly with use, and helps explain the discrepant battery life times seen by various users. Andantech summaries:
Apple's 5 hour claim is laughable but not as much as I expected. If I wanted to I suspect I could hit 5 hours by making the web browsing test less stressful, but my focus was on real world usage scenarios, not proving Apple correct. Regardless, 4 hours and 16 minutes doing what I consider to be the intended usage model of the Air is respectable. It's not great, but it's not terrible either.