Areation, before or after you pitch??

I went and watched my friend brew yesterday and he areated "after" he pitched the yeast. Im a newbie whos been refering to Palmers book and other various sources for my info and in the book it seems to indicate that the yeast is pitched after areation.

Which approach do you use?

I always do it before. When the wort's going in the Carboy.
I make sure my brews in it's resting place when I pitch.

Well, for my current Schwarzbier/Black ale experiment, I pitched the London ale yeast while aerating and the lager yeast before. The only problem I see in the timing is if you are sprinkling a dry yeast directly. If you aerate first, the yeast might get hung up on the foam.

I have used only dry yeast so far. I rehydrate it first. I got a system down that when the yeast is at pitching temps, everything else is ready to go. Pour the wort into the primary, dump in the make up water, that alone helps out with aeration as well. Pitch the yeast and then agitate it with my brew spoon, a lot, for about 5 minutes and then button it up. So far, all has been well.

I usually pour about half my wort into the primary, pitch the yeast, shake the crap out of it then add the rest of the wort.