Given all the hoopla surrounding the MacBook Air's battery life, I thought I'd throw my two anecdotal cents into the ether.
Jacqui Cheng's review was published the day before my Air was to arrive, and I was understandably unnerved by her description of the Air's battery life:
I'll cut to the chase here: the MacBook Air's battery life sucks. A lot. I found it to be a pretty big disappointment, holding it to my admittedly-high standards. I ran down the battery from full charge four times and came out with an average of two hours and 33 minutes.
She was, on average, getting half of the five hours claimed by Apple.
I took delivery of the Air on Monday and have run the battery down many times since, but never in under four hours.
So why is my battery lasting ~40% longer than Jacqui's? Well, one thing that the reviews seem to routinely gloss over is that the MacBook Air will likely be your second or even third machine (as I previously pointed out), and as such, you'll likely use it for mostly 'lightweight' tasks. AnandTech gets this right:
By now you've heard that under "normal" usage, the Air can only manage about 2.5 hours of battery life. That's true and at the same time it isn't. I touch on part of this in the review, but the MacBook Air isn't designed to be your work notebook - no ultra portable is. It's a notebook for a writer, for someone taking notes in class; it's a second notebook, or a third system. As such, the typical usage model can be very different than your standard notebook.
It will come as no surprise then that Anand's results were very much in line with my own: "...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." Indeed. Now, am I saying that Jacqui's results are flawed? Of course not -- those are the numbers she got doing what she typically does on that machine. I'm simply pointing out that the battery life is more than decent for my use case.
With regard to the specifics of my setup and usage over the last few days, I have the 1.8GHz/HDD model, kept the screen brightness at less than 50%, disabled Bluetooth, disabled Dashboard, disabled Spotlight, and always had myriad applications running. I didn't do anything too processor-intensive with it (and never expected to; see the footnote in my initial Air article) and was really obsessive about killing errant processes that were stealing too much CPU time.