What happens if 2 people share the same IP number?

[Anthea]

My friend's cousin is coming to stay with me

While he is with me would he be able to use my broadband connection to log on to this forum?

I know that in the past some people have played games on this forum by having several identities

One person used to keep thanking himself using different identities

[Piling]

He might also be register as a full member and we welcome him

Some people had already there common IP, or they use proxy. It has no effect, except if we decide to ban someone by IP but it never happened, I think.