Here is a related worry i have: if big retailers and similarly large corporations and institutions start accepting BTC transactions, many of the BTC will likely be funneled straight to the banks. The banks wouldn't have to *buy* any BTC at all. Then, having acquired all this BTC, the banks could just sit on it, and take the losses on the chin. It wouldn't take long before that would become a very big pile of bitcoin for them to sit on.
Retailers are not going to pass BTC onto banks when they can sit on an appreciating asset themselves for little to no cost (few security experts).