> I have a feeling that if I go credit I'd be allowed to overdraw my account that way, and incur fees (which the banks love) whereas if I go debit, I can't spend more than I have in the account. But I don't really know that for sure...

You'd think that's the way it works, and maybe it does with some banks. Ours lets you overdraw either way. We got slammed with three or four $20ish fees by using the card as a debit a few times one day when we didn't have enough in the count. I was furious and called to complain. The bank said they had sent documentation about how that works, so I should have known. Still, they took two of the fees away but warned they'd let any future fees stick. That was an acceptable compromise for me, but I'm still annoyed by it. I don't see that there is any reason to let a debit card overdraw, except that the bank wants to charge outrageous fees for screw-ups.

Anyway, for a card that can serve as both a credit and debit card, I don't think there is any real difference between doing one or the other. You get a choice, I think, only because some cards will only serve as one of the two and not both.

And, yeah, debit cards have been a pretty recent thing around here. I don't know that I've ever even seen a debit card that didn't also function as a credit card, unless you count ATM cards, which, until the last couple of years, only worked at ATMs.