Below is the official statement about the maintenance fee: The fee will be implemented on November 12th 2013.
The maintenance fee is estimated as $0.30 / kW*hour: $0.17/kW electricity cost + $0.09 data centre upkeep + $0.04 hardware repair/maintenance.
(The power consumption of 1 GHS is 1.5W per hour)
The fee will be billed in BTC per mining share. The estimated fee is 0.000000002695 BTC/share, which makes it ~4% of total mining profit.
The fee will be adjusted according to the BTC/USD exchange rate.
About the hardware maintenance: We will charge $0.09 for the data centre upkeep + $0.04 for hardware repair/maintenance.
Handling 600+ kW mining equipment is quite challenging. This involves MANY people working at the backend, who: Replace dead chips Fix PCB issues Upgrade electricity links Improve mining software to reduce stale shares (we have stopped delivering stale shares for purchased GHS).
The maintenance fee is only applied to GHS purchased at CEX.IO. (Personal miners are not affected)