So, here is what I think will happen.  Somebody will finally get serious and make a better bank than mybitcoin. Then begins the bitcoin bank competition. As a wise manager of money, I use this to my advantage and let them compete for my business. Vending machines will just need need these inputs from the user: the bank used ("MyBitcoin, Visa, MasterCard, etc."), user, pass, confirm. The vending machine will show the rates that they charge for using each bank as a function of how much the vending machine company trusts each bank. Think of bitcoin as gold and the online bitcoin banks as all the currencies in the world. I'm going to hold more of the currency that stays truer to the nature of gold.

I don't know how the interface would work, but I'm sure someone already figured that out.