I personally feel that its pretty overrated and that people with rear steer generally use it way too much and end up wasting time and screwing up lines by messing with their rear steering.
Here's one example from the magazine shoot during Easter this year:
4 wheel steer Jeep, 2.5 ton rocks, this may have been the Jeep on the cover I forget
[youtube]VRXL6jEB-SQ[/youtube]
He's screwing around with the rear steer a bunch, its not helping him. This guy (and the other couple four wheel steer Jeeps with him) spent a long time on this obstacle, at least 5 minutes each.
Mine, sans rear steer:
I made it in what, 10 seconds? Some of that is driver, and yeah, I've driven that trail a time or two. My point is this:
Rear steer is VERY useful in some situations. There are many obstacles (10+ buggy type stuff, generally) that absolutely require the maneuverability of rear steer. IMO, 98% of the time having the rear tires straight will treat you just fine.
IME, most people with rear steer end up screwing themselves by trying to use their rear steer when they don't need it.
Oh, and adding a steering D60 in the rear will open a serious weak point in your rig (or it will open a serious weak point in your wallet). Many of us are spoiled by having the near bulletproof FF 14 bolt in the rear; the D60 ring and pinion, joints, shafts, etc are much easier to break. They hold up well in the front because there is usually less weight on the front when parts are really stressed (i.e. climbing). Steering axles are much easier to break than non-steering axles, in general.
you make the heep look like a turd 
