I usually pay by credit card, for convenience and always for business. I will add the appropriate amount to the pre-tax total and charge it to the card. I know that tip will be shared with all the staff, and no problem with that.
But I have not dealt with all the staff, only the person who came to my table. Sometimes (often) that person is beyond exceptional, and I would like to add an extra reward for him/her alone. Also, they are usually younger (translate poorer) than I, and I know they need a few extra bucks more than I do.
So I try to do that with cash. If they will be picking up the bill and payment, I'll include a five or ten (or whatever) in cash, and tell them it is just for them. If they will not be picking up the bill I don't want to leave it on the table for the busperson to grab, so will try to find the waitperson before I leave and hand them the cash direct.
I am always thanked profusely, but sometimes I seem to discern a quick flash of confusion on the person's face, almost as if they are considering what should be the ethics of the situation -- keep the extra themselves, or throw it into the pot with the rest.
As I said, I do this ONLY because of the superior service, or even only friendliness, of the person at my table. If I knew for sure that money would not be all theirs I would probably stop this practice.
Any opinions from the pros out there? Would you keep the extra, or share it? I want the answer to be you would keep it (and would feel OK about doing so).