I have been looking into relative size/volume/surface area of the circulatory system in different species e.g. mouse & man. The only estimates that I could find all quote the same number (60,000 miles) without a primary reference or a plausible way of estimation. This leads me to believe that this is likely to be an urban myth, even though I can imagine the numbers could be quite high.
An adult human has been estimated to have some 60,000 miles (96,560 km) of capillaries with a total surface area of some 800–1000 m2 (an area greater than three tennis courts).