How should I sautee Portobello Mushrooms?
Mushrooms DO require a good amount of oil due to the fact that they will initially absorb it.  

However make sure that you're adding salt to them right away to help begin drawing the juices out and start them over high heat, making sure that the pan is "screaming" hot before you ever add the oil and the mushrooms so that it will retain the heat even after the mushrooms are added to the pan.  As the juices begin to exude from the mushrooms they will take the place of the oil and as the juices evaporate, the oil will aid in browning of the mushrooms.  

As they moisture begins to evaporate you can begin to decrease the temperature to avoid having to add more oil and keep them from sticking to the pan.  I think mushrooms taste best when they've been allowed to cook to the point where the moisture has evaporated and a really good browning has taken place (not burnt of course).