What will be the value of one Bitcoin when the number of users (people that will want to use Bitcoin) will hit 21 millions?
At this point, if each user wanted to have 1 Bitcoin, will have to pay a certain number of $ or or Y, whatever. I'm going with $ just because it's the most used around the world.
How many $ do you think that person, the n. 21 millionth, who wants to buy 1 BTC will have to pay to obtain it?
My wild guess is: 160000 $.
If we were to have 21 million bitcoin users, the prices will surely sky rocket, but I think that just means we begin trading more in Satoshis than using bitcoins as a regular trading unit.
I really look forward to such a day

Wild Guess: 10k$ per btc when the users reach 21 million.
Most actual bitcoin users today can say that they own at least one bitcoin.
If we have 21 million users that can no longer be said. Several people own more than one bitcoin and there are lost coins.
21 million users should push the price well over $10,000 IMO. The fear of missing out will mutate into crazed hoarding. Many will refuse to sell, pushing prices/value even higher.
totally not true. Most bitcoiners own less than a bitcoin even now.