Each blockreward is 25BTC=$11,000
It would cost at least $55,000 for someone to unspend a txs that is buried 5 blocks deep.
What if Satoshi decided to move $1,000,0000,000 of coins at once?
It would take 90,909 blocks of confirmations before we could trust the blockchain again, 631 whole days.
Before then, it would still be profitable for satoshi to buy massive amounts of computers, and to build a fake chain from before he spent the money.
If satoshi did build this fake chain, it would undo every transaction.
If someone spends a massive amount of money, it leaves bitcoin in an unsecure state for a long time.
consider also that platforms like Color Coins and Counterparty can potentially make transactions that are worth more than all the Bitcoins in existence!
not to mention that these are TRADES and it's possible to reverse market rallies and collapses.
we're discussing this here:
https://bitcointalk.org/index.php?topic=613643.msg6824824#msg6824824add to this the fact that hashing power is now a commodity that is brokered and transfered very quickly, and I don't even need to procure hardware, just rent the hashing power for a day or so(thus the estimate to execute an attack is even lower).
-bm