... There's only 11 million bitcoin addresses;
There are 2^256 bitcoin addresses.
Just a example of how much 2^256 is:
If you would split each of the possible 21 million bitcoins in single satoshis and place them in their own bitcoin address, the probability of guessing such an address would still be 1.813595x10^-62
I thought it would have been clear that I meant the number of bitcoin addresses
used (nevermind that 90% of them are empty), not the theoretical limit. I was under the impression that there were 2^160 possible (2^256 for public keys).
Though digging around I may have been looking at old stats... I believe the 11 million number was from April 2013.