In my experience, taxi drivers know where they're going. I always use pretty major landmarks to tell them where I'm going, but all the cars are equipped with GPS to put in the address if it's necessary. I went on a quick trip to Daejon last weekend and I must have just had bad taxi luck. The first cab I got into seemed to understand where I was going. He questioned what I said a few times so I kept repeating myself and just said, "Nayyyy," (yes) when he asked me questions because that's what I do... Well he didn't know where he was going. In fact, he drove me to the opposite side of town and then back when I finally got a hold of someone to tell him where to go. $12 wasted... Oh well...
Then I'm going home and get in a taxi to take me to the bus terminal. There are more than one bus terminals in the city so I said "Express Bus Terminal" (with a Konglish accent, of course) and he had no clue. I tried to play the gesture game and use my limited Korean skills. He started driving, but I was well aware he had no clue where to take me. I decided I didn't want to take a trip around town again so I just hopped out and got on the phone for some Korean help. My next driver was wonderful.
In addition to GPS, most taxis also have TVs in them! When I first got here I was definitely alarmed when a driver would watch TV while he was driving. Now I'm completely comfortable with it and even enjoy it. It's fun to make up English dialogue to what they're saying. My driver that particular morning was wonderful because he even switched his TV to CNN in English for me! I've had drivers put on special English music but English TV was a first for me. So we rode to my destination enjoying the speech from the Australian Prime Minister. Take a look... (this wasn't my driver but you get the picture..)
No taxi ride in America will ever compare.