I go back to the comment upthread about the wallet: if I don't have to pull out a credit card to pay for the drink, it seems awkward to pull one out to pay for a tip.

I hardly ever carry cash...definitely not $1's by habit. Would a bartender be happy to swipe my card for a $1 tip? Could he even do it with no underlying charge? If I order a round of drinks for a table full of people, then I'd probably insist that he run it for $5-10. But solo guy, drinking one pint of beer...what's the etiquette say to do? I'd willingly tip if I had an easy way to do it.