We were just discussing this earlier with some friends. Don't bitcoin transactions take a large amount of time? A block takes 10 minutes to mine, and there is no guarantee your transaction will be picked up by the currently mined block (or the one after), because there is a limit on the number of transactions that can fit in a block. Are there solutions to this?
Ethereum's blocktime is way shorter: 10 seconds. You usually want multiple blocks to be finalized, from 3 to 6 to be sure you are on the longer chain.
The proposed blockchain solution for this are state channels where payments are then instant. Using state channels you can build a multi-hop network solution called Raiden (Ethereum) and Lightning Network (Bitcoin).
By that standard, when you use a bog standard Visa card you're not actually paying with dollars[1], you're paying with the artificial virtual currency your bank provides that is pegged to the dollar at 1:1, and merely funding your account with dollars.
No, you are paying with whatever currency the counter-party accepts. What backs the debit/credit card does not matter as long as the issuer thinks you have the assets to cover the loan they are making. If I have a card linked by my brokerage account I am not paying for dinner with shares of AMZN, I am paying in dollars and at some point will be required to convert some asset into dollars to cover the loan.
But this is a pretty inconsequential semantic difference. You could just as easily say that you’re selling dollars and the grocery store is paying you in bread.