I hadn't thought about it, and to be honest, I saw the title of this tread and purposely didn't read it for a few days for fear everyone did tip the driver ("you don't? d'oh!") and then I'd feel just horrible! But, I braved up, saw it wasn't the case, got relieved a bit, and then figured, well, why not? I tip other folks, why not these guys who frankly do a lot more, and more politely, than others?
Okay, I had to laugh. I hate typos, but I decided to leave this one. tread=thread - makes me sound so Irish!