Some people have been threatening not to buy, and others have been saying that they will buy two copies.
Remember that you can only play one copy at a time, so if you have multiple computers that you want to play multi-player on against people who don't have their own copy of civ 5, you will need extra copies. So there may be a practical reason to buy two copies.
The rule is, you can have one Civ V per account, one account per purchase of Civ 5, and an account can only play civ multi-player on one machine at a time. You can have multiple accounts. You can install on multiple machines with only one copy, but each computer has to be validated via steam, online. This has all been officially established.
Poll pending.
Remember that you can only play one copy at a time, so if you have multiple computers that you want to play multi-player on against people who don't have their own copy of civ 5, you will need extra copies. So there may be a practical reason to buy two copies.
The rule is, you can have one Civ V per account, one account per purchase of Civ 5, and an account can only play civ multi-player on one machine at a time. You can have multiple accounts. You can install on multiple machines with only one copy, but each computer has to be validated via steam, online. This has all been officially established.
Poll pending.