As a person attached to her car ever since she got a driver's license, I must say, I am enjoying the public transportation options that Istanbul has to offer. I still do not recommend anyone to try to use the public transportation during the rush hours (yes plural in this city!).
However, if you are flexible as I am, there are plenty of options in this overly crowded and busy city. For instance, tomorrow I have a few errands to run around the city. Here is what I am going to do:
I will take my car to the Kozyatagi Metro station which is about 5 minutes from my home. I will take the Metro (the Tube if you are British, the Subway if you are American) all the way to Kadikoy. I will hop on a ferry to Eminonu or Karakoy and walk to pick-up my prescription glasses. I will then take the Tram to Kabataş and ride the Funicular to Taksim where I will get on the Metro to Mecidiyekoy to visit a friend at his office. Then, I will probably take a taxi to Okmeydani to a hospital in order to visit a very close friend who will be out of surgery hopefully by then.
The best thing is that I use an Istanbul Kart on all these vehicles which makes it real easy.
If I take my car, all these are still doable but the amount of time I would spend just sitting in my car and the stress of finding a suitable place to park does not make it logical. Besides, I love having tea on the ferry crossing the Bosphorus and I will make sure I will post some photos later in the week. And of course, this not only saves time but plenty of money as well.