/napkin_math_when_1_of_todays_internet_business_is/]Napkin Math: When 1% of today's Internet business is conducted using Bitcoins then the worth of 1 BTC will be 402€
I think you're assuming that each bitcoin will only turn over once per year. If you assumed that each coin would be spent once per week, you get a price of about €8.
Maybe a more correct value can be in the range 16-24$: is true that bitcoin can flow really fast with 1% of internet business, but also you've to think that a smaill percentage (2-5% I presume) of bitcoin was lost due to missing/damaged/forgotten wallets, and another 10-15% is not used for transactions but as personal reserve. And again not all the people who use bitcoin will use them weekly on internet. If we can add to the internet transaction a 0.01% of the "real life" transaction we can easily jump over 50-100$.
Another good marker of the possibile value of bitcoin is the number of people that will use them: if there will be 1 million of user each of them can have 21BTC in average, but if users will be 10 millions or 100milions (10% of the population of USA and Europe or 1,5% of world population) the average will drop to 2 or 0,2BTC. In last case the value shall be over 1000$ to make them still usable (it will be a mere 200$ for every user - that are penny in the pocket in a real market).
And don't forget that 21 milion of BTC will be mined only in 2140. Now we have less than 7 million, and when there will be 10 million out i you've to double all the math.