One of their main problems is that, as you pump enough energy into them to justify their cost compared to other storage mechanisms, the spinning mass becomes more and more of a danger if it ever breaks loose. Not to mention the gyroscopic effect making a “fully charged” fly wheel very hard to safely move.
Spiral galaxies like the Milky Way are surprisingly rare. Astronomers may finally know why. (www.livescience.com)
What are some promising solutions to solar power's lack of night time availability? Is "transoceanic power transportation" on the list?
EDIT: Submarine power transportation is indeed on the list...