In all seriousness, using cards used to be super-fast. Remember those Visa commercials - swipe and go, swipe and go, oh no someone with cash ugh it will take forever.
Now in CVS I have to swipe the card, tap NO (I don't want to donate), YES (this is debit card), my pin, YES (is $9.75 correct?) and then wait for transaction to be completed. Meanwhile a guy next to me handed $10 bill and got quarter back. He left before I finished swiping my card..
Donate?! WTF, go away. I want to swipe and go, damnit. I didn't come to your establishment to take part in your charity drive.
Debit? Credit? WTF, can't you tell?!
Is this the correct amount? Shit, I don't know. Did the computer add correctly? Is this a bartering interface, where I get to say "NO", and make a counteroffer? No? Then why the hell are you asking me when I don't have a real alternative choice to make?
My personal supreme pet peeve is going to a gas pump, pressing the credit button at the pump (which has both credit and debit buttons), then being asked if the credit card I just swiped is in fact a debit card.
Why I think that screen is there is to shield a merchant from someone coming back after the purchase to complain. And I doubt any merchant would use that confirmation to defend an error and risk losing a customer. Which, to me, makes it even more useless.
No, they can't tell when the same card can be processed in both ways. Just for fun, check out your bank's debit card fraud protection details - odds are you're much better protected if you run your debit card as a credit card (i.e. no PIN, but a signature), that way visa/MC takes on the fraud risk.
Also, on some rare occasions when I use my debit card, the PIN entry pops up without prompting. If I don't trust the place or don't want to divulge my PIN to prying eyes, I have to hit a cancel button to process as credit. I've never seen a PIN prompt show up when swiping my credit card. If they can't tell, how does the terminal prompt for PIN only when a debit card is swiped?