Considering the amount of users of vanitygen, and the fact that each user is generating millions/billions of bitcoin addresses, won't we run out of bitcoin addresses soon? What would happen if we did run out?
There's no problem with running out of addresses. The identifying part of a bitcoin address is a 160-bit hash. 160 bits gives in the range of 10^48 addresses, or roughly 1 for every atom on the planet.
Amount of Bitcoin addresses is allways same with or without vanitygen.
If someone generate address with vanitygen it's NOT RESERVED only for him… everyone can generate same address and using it too. Because It's only secret key and address, which can be generated from secret key (2 adresses from 1 key).
But there are lot of possible adresses, and it's almost impossible to randomly generate the same address as someone else.
vanitygen doesn't bother saving all of the addresses it goes through to generate the one being searched for, so the person running vanitygen doesn't really "get" those addresses.
Addresses are never marked as "taken" in Bitcoin. The only thing identifying who "owns" an address is who has access to the private key.
If vanitygen doesn't give you all of the private keys for the addresses it searches through, then those are still not "owned" by you or anyone else.
We will probably never switch to a new key format because we run out of keys, or because computers become powerful enough to steal bitcoins from old keys. There's 160 bits in RIPEMD-160, and even building a computer to count from 0 to 2^160 is beyond current technology.
We might, however, switch to a new format because of a vulnerability found in ECDSA or RIPEMD-160.