Very little... almost nothing! Way less than what Tyler Bracken mentioned he is making.
Having said that, I hub mostly for fun than to earn money. I don't take the time to promote my hubs through SheToldMe etc etc because that feels like work to me not fun. So, I think someone could earn much better than what I am making from hubbing if they write hubs more frequently and look at ways to improve traffic etc. I just like the fun factor of having control over the layout of my hubpages.