well i know that space shuttle looks tiny... so i bet its pretty far away.. i would have guessed 50-60 miles away.
also, i found this interesting:
FAA Part 91, Part 125, general aviation and VFR operations are prohibited within a 30 nautical mile radius of Launch Pad 39-B from the surface to but not including 18,000 feet (located on the Melbourne VOR/DME 004-degree radial at 30 nautical miles). Among the general aviation airports affected within this area are Space Coast Regional Airport in Titusville, Arthur Dunn Airpark in Titusville, Merritt Island Airport in Merritt Island, Rockledge Airpark in Rockledge and Massey Ranch in Edgewater.
Within an airspace radius between 30 and 40 nautical miles of Pad 39-B, a discrete transponder code must be obtained and clearance granted from air traffic control before entering this airspace. Continuous radio communications must be maintained.
http://www.nasa.gov/centers/kennedy/news/releases/2005/58-05.html