I have included a section on how pumped hydro power can be used to balance the generation of wind power on my Sustainable Energy page. (ramblingsdc.net)
The main disadvantage of a water - balanced railway (just like any other use of hydro power) is that it can not be operated when the water freezes over. (lowtechmagazine.com)
It may have its flaws, but there's no denying the amount of fun you'll have boosting past your opponents on your rocket - powered hydro jet. (videochums.com)