Hmm... Even 5 hours is pretty low compared to what I get under OSX with normalish usage on my MBA 11". I've also found that I get markedly better battery life when I connect to my Apple-branded wifi base station than when I connect to wifi just about anywhere else. This makes me wonder if Apple doesn't have some proprietary power scaling stuff with the wifi. Still, 5 hours is good enough that I might consider a more thorough checking out.
EDIT: I should add that I've only spent time in 10.9 on this MBA 11 2013 model. I've been told the battery life in 10.9 really is quite a lot better than in 10.8.
Well, with comparable usage I was getting perhaps 20 extra min on OS X. It's very good I think. It's pretty clear when you check sensor temperature: both machines are equally cold.
In the old (and not so old) times, laptops with horrid Linux power management would be extra warm due to all components being powered up all time. Far from it right now, if you cherry pick hardware. There's still room for improvement, though.
EDIT: I should add that I've only spent time in 10.9 on this MBA 11 2013 model. I've been told the battery life in 10.9 really is quite a lot better than in 10.8.