Marc - we took a little drive over to the Asian side last year on a Sunday morning on our day in Istanbul on our Cappapdocia pre-tour. The guide said that early Sunday is the only time to drive it - otherwise the traffic backs up for hours, so I would do a ferry rather than a taxi if you want to go over there. The areas we saw were residential, no sights, so I don't think it is worth taking the time since there are so many interesting things to see in the city.
