I don't know how to get started counting... but let say if we have 7 billions users (the population of the whole world) and each generated 10k addresses, which will give 70 trillion addresses used/ever generated.
(70,000,000,000,000 / 2^160)
= 10^ [log (70,000,000,000,000)- log (2^160)]
= 10^ [log (70) + log (10^12) - 160 log (2)]
= 10^ [1.845 + 12 log (10) - 160 x 0.301]
= 10 ^ (1.845 + 12 - 32.164)
= 10 ^ -18.32
~ 10^ -18 x 100%
~ 0.0000000000000001% of all addresses
~ 0%
I think I am over-estimating but we are dealing with huge numbers...