The P-3's don't really focus as much on finding submarines these days, but are primarily involved in reconnaissance missions, maritime patrols, anti-narcotics trafficking operations, and search and rescue. I live near Brunswick NAS which is a P-3 base that deploys squadrons to Bahrain to fly missions over interior Iraq.
If you see a P-3 on the East coast, it's usually going to be out of Jacksonville NAS, FL, or Brunswick NAS, ME. Not sure if there's still a reserve squadron in Pennsylvania, but there was at one time. There's also bases near Seattle, Washington and in Hawaii.
I see the P-3s all the time flying around on training flights in the interior of the Western Maine and New Hampshire mountains far from the ocean. Most likely the one you saw was from one of the first two bases I mentioned, and it was probably on training missions of some sort and decided to shoot a few approaches for the logbook. They do this all the time at PWM, PSM, and BGR, so perhaps they coordinated Ashville into their missions? I even saw one at BOS one time long ago!
[Edited 2008-03-27 19:22:00]
[Edited 2008-03-27 19:22:24]