A great topic!
On planes...
I try to make conversation with seatmates in F. If I am travelling Y it doesn't seem to flow as easily.
I have met a lot of interesting people. One time I had a long conversation with the president of a very large chain of auto dealerships. Other times with people in high tech businesses similar to mine.
The best time I had was when I met a very very well known former presidential candidate (whom I did not recognize at first -- that's just me) and we chatted it up. Great fun!
But after a little testing, if the person next to me doesn't want to talk, then I don't talk. I always bring several books along and things to do.
On the ground...
I try out interesting restaurants if possible, but I don't have time for anything but business and I have no interest in talking to people in hotel bars, etc., so I always bring a book along when I dine. I love to read and eat by myself, so it is a pleasure.
Communicating with people on Flyertalk is a great way to stay connected when somewhere else, and I find that email in general makes me feel more connected on what otherwise can be a lonely business trip.