Yeah -- this would be really important to know. If you process a tax payment on payUSAtax.com with a debit card, you have to specifically identify it as such, I think. Does it ask for your pin? If it does, it seems to me that would disqualify it from most debit card T&Cs for miles. If it doesn't, then I would think the web site would charge you the credit card payment fee.

Wish we had some more data on this. I'm just waiting for the right opportunity to sign up for a debit card deal. This would make it worthwhile.