My best estimate is around 1,000 miles, of top-down, trouble-free driving.
In the hills of Eastern Ohio, there are lots of roads that are a treat to drive. One of my best friends is a muscle car enthusiast, and, during the warmer months, we had a Sunday morning (after church, of course) routine of taking our cars for a 40 to 50 mile cruise. We were quite the "odd couple;" a white over red Tr-Carb being followed by a yellow and black '68 Plymouth Roadrunner, or vice versa. Those trips had to account for 700 miles of the total, and all the miles I drove were within 50 miles of home.
For 2007, I resolve to drive my car lots more, and as soon as I finish with this post, to write down my odometer mileage, so that I can better respond to a similar question at the end of the year.
Jerry