To expand on one of mthayer's points a bit, if you are touring in the offseason (fall, winter, or spring) and plan to use routes that include ferry rides, make sure that the ferry is running during that time of the year. A planned visit to Block Island (in the Long Island Sound) during my first tour was eliminated because the ferry service didn't begin until two weeks later.

Also, make sure that your maps are up to date. On another tour of mine, along a designated bicycling route in North Carolina, the road went underwater because a dam had been built after the map had been printed.