Similar topics have been brought up several times. If my calc is incorrect, I'm sure someone will correct me.
A satoshi is this part of a bitcoin = 0.00000001.
This means that there are 100,000,000 satoshi's for each bitcoin.
This means that when all the bitcoins have been mined, there will be 2,100,000,000,000,000 satoshi's around.
If there are 10,000,000,000 people in the world at that time, there will be on average, 210,000 satoshi's per person.
If a satoshi is comparable to a peny, each person will have, like $2,100.
If this isn't enough, the devs of future Bitcoin clients can divide the satoshi as greatly as necessary.
Take a look at
http://gizmodo.com/5995301/how-much-money-is-there-on-earth, and do the calculations to see that there is a lot less money around now, than there will be in satoshi's once bitcoins are all mined.
