So, I was thinking about the address generation scheme that is used for Bitcoin. Please note I did not do any math here yet to see if it is likely to happen, it's just a concept.
From what I understand, the keys are 256 bits (10^77) and there are what? 1 billion keys?
http://en.wikipedia.org/wiki/Birthday_paradoxhttp://en.wikipedia.org/wiki/Universally_Unique_Identifier#Random_UUID_probability_of_duplicates1-e^(-(n^2)/2x)
EDIT:
1-e^(-(1000000000^2)/(2^256)) =
1-e^(-(10^18)/(10^77)) =
1-e^(-1/(10^59)) =
10^(-60)
Current Block Probability: ~ 10^(-16)
So, getting the block is 10^45 times more likely than a single collision. An attacker would have to hope for colliding with wallets containing trillions of times more coins than will ever have been created. But if an attacker can change the value of 'n' to 10^39 (duodecillion attempts) then he'll likely be quite profitable... but then again he'll only be colliding with his own keys.