Nothing-at-stake solved.
http://satoshifantasy.com/bergstake-2/
http://satoshifantasy.com/breakoutcoin-with-bergstake/
The first question that comes to mind is how does one prevent the transfer of the bergstake?
its not a currency, its locked onto the original address, so only way to transfer is to share the private-key.
So what happens when the original bergstake holders die? I can see an attack here. Sell heavily discounted mining equipment to people with very low life expectancy, wait for them to die and then launch the attack.
it becomes an inheritance. seriously, if this is the only attack, we are in great shape!