I don't know what kind of CNS damage high rep leg sled is going to do. I mean, it isn't like doing a 60 rep 265lb squat... in fact, I would say that it is a good bit easier than even doing a 60 rep bodyweight squat.

I think that Eric is referring to the rather poor design of many leg presses which actually promote back rounding (maybe the tester thought this was more comfortable? Who knows). Anyway, I would just do my best to keep my hips down and tight. You don't want any weird inch worm crap with your lumbar region. Not even under that light load.