The value of a money is what one can expect to gain in exchange for said money....
I am not worried about people dumping BC's on your exchange, I am saying any value is arbitrary until people come to accept BC as a medium of exchange...
I don't think their value is arbitrary. Just really really small. A medium of exchange or currency needs to have a "stable value" or at least a value that can exist within a certain range for an extended period of time. This builds trust. When there are multiple exchanges trading Bitcoins and each exchange is tracking a similiar exchange rate it will build trust. Eventually it will reach a critical mass.