Another question. Are you supposed to do this before or after you chill? I did it after I chilled it.
Depends on how you're chilling. If you are using a plate or counterflow chiller, you can whirlpool hot which leaves the hot break and hop material in the boil kettle (and the cold break ends up in the fermentor unless you let it settle out in another vessel or dump it if you have a conical fermentor).
If you are using an immersion chiller, you'll be whirlpooling cold. I can get a decent trub cone when I whirlpool cold, but the cold break is pretty fine and once the wort level drops below the top of the cone, the cold break tends to slide down towards the wall of the kettle. A little cold break in the fermentor is no big deal though.
Check out Kai's page on whirlpooling for more info (including an interesting section on whirlpool dynamics): http://braukaiser.com/wiki/index.php?title=Whirlpooling