I have yet to get any ND filters after I was told one was $50 at the camera store.
I will get them eventually, but I at least want to be able to experiment and see what they can do, or not do, for that matter. I wonder though. The ND filter will allow longer shutter speeds, but aren't we still dealing with a wide range of light and dark that we just don't have the range for anyway?
I think the neutral density filters can reach up to 4-stops but I remember reading in Understanding Exposure that all you really need is a 3-stop filter and he was using his filter for real stark contrasts. If you own the book...he talks about it towards end, if you do not own the book I recommend picking it up!!