More details on my aeration experiment...A co-worker/friend/ fellow brewer and I had a discussion one day concerning whether or not we were getting complete aeration of our beer wort. The next time we had some down time in the lab we ran a little test comparing funnel addition, stirring and sparging/stirring (i.e. airstone) affects on DO2. Starting with de-gassed water we measured the DO2 with calibrated meters before, during and after using these three methods. Not surprisingly, any of the three methods will fully aerate your wort. But, there is a difference in how quickly the liquid is aerated. The funnel method aerates the fluid as you add it to the your vessel. Vigorous stirring and sparging/stirring both took longer (and were comparable time-wise) but the sparging method was obviously easier on the arm. None of the three methods is going to aerate to a higher degree than others since once you reach saturation, you can't go any higher...Unless you were to sparge with pure oxygen. However, this has it's drawbacks since pure oxygen is toxic after you reach a certain point.
As Oskar said, it is good to think of oxygen as a necessary nutrient. One additional note on the importance of a good primary fermentation...It is vital to produce not just a big population of cells, but a healthy population as well. Specifically, it is important for the yeasts to assemble a good lipid layer in their cell wall. Without a strong lipid layer, the cells become less tolerant of alcohol concentration in the secondary fermentation...Regardless of advertised resistance. This means that instead of a good strong completion of your secondary fermentation, the cells will begin to peter out after 5%-7% alcohol conditions are reached.
Peace.