How improbable is it? According to US statistics (taken from here http://en.wikipedia.org/wiki/Demographics_of_the_United_States#Demographic_statistics
), there are 245,267,292 people above the age of 15. In 2006, there were 21.7 billion credit card transactions in the US. If bitcoin replaced credit card usage but stayed at the same frequency, that would equate to roughly 231
new addresses created every year, since the bitcoin client creates a new address each time.
Hm...maybe not as big of a deal as I initially thought. In order to run out of addresses, which I think I read have a maximum of 2160
, at the 231
rate of creation, it would take 6.8 x 1038
680 undecillion (thanks, wolfram alpha) years to run out of addresses. If we assume that the world consists of more than the US, and double the number of transactions, it would still only be 232
and not make any real difference. If we assume that everybody on earth does the same amount of transactions as Americans, that would result in 667.5 billion credit card transactions each year. This would mean it would take 2.189 × 1036
years to deplete the available bitcoin addresses. Even if the amount of yearly transactions increased by a factor of 12, it would still take 1.824 x 1035
years to use every available address.
Incredibly improbable that somebody will run into somebody else's address, even after 10,000 years. Probably just about as improbable as Mr. Lucky in that other thread finding all the remaining blocks.