Did you have to reduce the distance you run when you first got them?
well, it says to do 1/2-1 mile per run the first week or two just to get used to it.
being a true getbigger i did 2 miles the first day.  i flew.
the second day i could barely walk.  it felt like someone hit me with a car.
so yes, i'd suggest 1/2-1 mile per run the first week  

but on week two (i run about 4 miles) i cut almost 5 minutes off my time just due to sheer lightness of the shoes.  i'm not sure i'd recommend it for heavy gravel running, but i run on pavement and even though it's a weird feeling compared to a normal shoe, it feels more natural after a few runs.