Keys (including private keys) are sent unencrypted, so in general it is recommended to
buy small amounts of bitcoins (due to lack of email security) and wallet should be swiped as soon as possible.
If some
small fraction
of the people holding gold (say, 5 %) sold their gold for US Dollars (releasing $ 400 bn), and the USD proceeds were used to
buy bitcoins, the total value
of bitcoins (commonly referred to as «market capitalisation») would increase by that
amount of dollars ($ 400bn), and because we know the total number
of bitcoins in circulation, we can derive a price per
bitcoin.