No, I left the brightness alone. In fact, the only thing I did was shut off sleep mode when on A/C. Now, this is the i3 model and the CPU uses a lot less resources than the i5 and i7.
The battery will click down when doing a lot of web browsing or listening to music. Did not pay much attention to video playback but did watch one movie and one TV show and the battery level barely moved.
It is possible that I may have a rare machine that has no defects or that the i3 models have no issues compared to the i5 and i7 models.
As for 8 or 9 hours of use; I think that was from one test bench model (i3) with nothing attached to it and all they did was turn it on and clocked it. Not connected to the Internet either.
Only an ATOM processor could be productive and provide a 9 hour battery life. I have the Asus T100 that gets 11 hours and I tested that 4 times and it actually does it.
I would say that it would be normal for the i3 to get about 6 to 6.5 hours, i5 about 5 hours, and the i7 about 4 to 4.5 hours with normal use and being conservative.
Now, if you shut the brightness down too much, it becomes not useable in a normal sense. It is actually not worth it and the light panel is LCD and uses very little power.
Now, I did not detach the keyboard/cover and tested the duration of the battery that way. I probably could get more by doing that. I also don't use OneNote and barely use the pen at all.
My email is POP3 so it pings the server in milliseconds and should not even register power usage.
So, if I did go more conservative, I could probably stretch the power consumption to 7 to 7.5 hours (possibly).
The type of program that you are running and the way it was coded is very important, just open Microsoft, don't play, leave it idle, turn off everything else you can and you will get 4 hours of battery at most.