Other than a brief and polite acknowledgement I mostly prefer to be left alone. But that's just me and it's a big diverse world out there.

Here are some other similar past threads. Personally I remain mystified at the popularity of the topic. Seems that traveling on airplanes requires the same social skills used elsewhere in a world populated with strangers.

http://www.flyertalk.com/forum/trave...ing-plane.html
http://www.flyertalk.com/forum/trave...st-flying.html
http://www.flyertalk.com/forum/trave...-seatmate.html
http://www.flyertalk.com/forum/trave...you-board.html
http://www.flyertalk.com/forum/trave...ny-i-work.html
http://www.flyertalk.com/forum/trave...ght-ahead.html
http://www.flyertalk.com/forum/trave...seat-mate.html
http://www.flyertalk.com/forum/trave...you-alone.html