In order to "power down" you must have 10x as much as you started with. Here is the official notice:
"Account registered by another account requires 10x account creation fee worth of Steem Power before it can power down"
Try for yourself... you can't extract your money until you have a MINIMUM of currently $160 usd in steem...
This means that every new steam addition will need 10x as much steem in order to power down... meaning if everybody pulls out and powers down at the same time, steem will crash...
Just a grave warning to you all.
Be safe with your money.