Leave it however you are paying (cash, cc, whatever).
This was mentioned on another thread (maybe the old board ?), and I am not condoning this
, just explaining a possible reason for the behavior......
I waited tables for 10 years. In the myriad of restaurants I worked at, the reason most gave for preferring cash tips was so they could fudge their taxes. The idea that they "get their money that night if it is in cash, and if credit it takes longer" is usually crap. In every single place I have ever worked, I got all my money that night regardless of the payment form. The only time that varies (in general) is when the server is working in a tip out function (IE: a bartender) where said person gets a percentage of the other servers' tips. This is usually paid the next day after all tip outs have come in.
Credit tips are automatically reported when the check is paid. Cash tips are put in based on what the server tells the computer when they clock out. The total is reported in by the workplace. Most server checks (at least in my part of the world) are generally next to nothing or void checks because of the taxes taken out. Therefore, servers generally end up owing in April on their returns. In the higher end places I worked in, some servers would owe somewhere around $600 to $1000 dollars to the government at tax time.
Do what you will when tipping, whatever you are morally comfortable with, but I tip the way I pay. Cash for cash, credit for credit. If you want to "serve" the waiter/ress best, then leave at least 20% for great service, and they will appreciate that.
Hope that wasn't too long winded........