Passive rear-wheel steering is a marketing term coined by Subaru for what the SVX's rear suspension does. But I'm almost certain that it works the opposite compared to how Harvey explained it. As the rear suspension is loaded up, for instance during a turn, the outside rear wheel (moving up) toes out and the inside wheel (moving down) toes in.
The reason it does this is that the two parallel links are different in lengths. So as the suspension moves up and down the hub is turned as if it was being 'steered.'
I don't really consider this steering, and it's not the first suspension scheme to do what it does. But it's still cool. Of course it means that when the rear suspension is loaded evenly, like during acceleration or a big bump, both wheels toe out.
I put a picture of the rear suspension in my locker:
http://www.subaru-svx.net/photos/fil...kets/17218.jpg
Edit: Well, I read the Guide's section on suspension and it seems that I had it backwards. During cornering, the Guide says that the outer wheel toes in and the inner wheel toes out. The Guide claims that this makes the car more predictable. In this case, I think 'predictable' is just another word for 'understeer.'