My 1991 Nissan 240sx had four-wheel steering. They called it "Super-HiCAS". A friend of mine with a 240sx with normal steering and I swapped cars to compare the effect. In "normal" driving, the differences are real, but subtle.

Given all the other features that may or may not show up on a car (anti-lock breaks, traction control, all-wheel drive, in-dash MP3 players, etc.), I'd rate four wheel steering pretty low on the list of desirable features. It's just not that big a deal and I suppose it's really just one more part that can fail (not that I had any problems with it; it's a very simple system if you look at it -- a servo motor centered between the two rear tires with connecting rods that let it "steer" for you).

Dan