No matter what, I always ask the driver to estimate the cost to my destination before I get in. If they can't/won't do it, I let them know I will get a cab who can.

If they can't do it, it either means that they're too inexperienced and have no idea where it is, or were going to pull a fast one. Since almost 100% of my biz travel is int'l, it's usually that they'll pull a fast one and overcharge. (every country except Japan whose drivers are extremely honest)

However, if you have at least some estimate, you know that you won't pay more than x amount. This way, the driver will do his best to get you there quickly. AND if he didn't know, at the very least, he would have had to consult GPS to give you an estimate, so you're forcing the directions!