I get 6-8 hours out of my Zenbook with ArchLinux. Nowhere near the touted 9 hours of the specs, or the 12+ of the Macbook.
My system is exceptionally lean. I run bspwm and the radios are always off except WiFi. Still, I feel like I could get a lot more from this laptop. I cannot (and I certainly wouldn't want to) install Windows on dual boot to make a comparison though.
What distribution do you use?