I obey the keep right rule at NLEX.
I have a question though: What if you're overtaking a long series of trucks or other vehicles (e.g. 6 vehicles) and it will take you approximately 10 seconds to overtake each vehicle. Do you
a) keep the left lane until you are through overtaking all vehicles, or
b) move to the right lane after overtaking each vehicle and only return to the left lane when you are very close to the next vehicle you want to overtake?
I often stick with option "a," unless there is a much faster vehicle breathing down my tailpipe, in which case, I let it pass first before resuming my overtaking maneuver.