Once bitcoin has replaced VISA, you'll probably not make a substantial profit of bitcoin anymore, but you'll still want to buy it because of the utility it brings.
Can the bitcoin network support the volume of transactions it would take to replace VISA or any other major credit card? The Visa web site says they process 150 million transactions per day
http://corporate.visa.com/about-visa/technology/transaction-processing.shtml. Is there an practical upper bound on the transactions/day for the bitcoin protocol? I imagine the block chain would get enormous very fast at that volume, but I'm still a newbie so I may be missing something.