Thought I'd weigh in on this little discussion, while I'm not a driver myself it does irk me that some passengers just treat them as part of the furniture. Just because it's his job doesn't mean you don't have to acknowledge him... at the end of the day, he is doing you a service. I always try to greet my driver when I get on, I just feel it's the right thing to do. And if it's possible, I try to exit at the front, so I can wish the operator a good day as I leave. If they don't respond, so be it, but I just think it's right. B/Os are people too.