New reply to an old thread.. I have three German Shepherds so you can imagine how much dog hair I get in the back of my Legacy wagon..
The BEST tool I've found BY FAR is a Zoom Groom.. A hand-sized rubber grooming tool intended for removing undercoat from the dog. Turned on it's back and dragging it across the carpet brings all the fur to the surface making it a snap to vacuum out. The trick is to drag with enough pressure to bring out the dog hair but not so heavy that you create too much friction and the rubber burns into the carpet.
I've been using this method for tens years or so....
