It depends on who I'm next to. I'm generally introverted and have other stuff to do on planes, but I've had very interesting flights talking with four seatmates I remember, three of whom initially seemed unlikely candidates for this sort of thing:

1. Dave Johnson, of the "Dave and Dan" decathlon buildup to the 1992 summer Olympics. He was interested in my early Apple Portable. I said something about its weighing 16 pounds. He said that wouldn't be a problem. I didn't yet know that he threw 16-pound weights for a living, throwing them further than many of us could carry them.

2. A stockbroker who began the flight by taking out thick financial reports and reading them as if they were really interesting. I pretty much gave up on her, but we ended up having a fascinating discussion of (among other things) Hindu astrology.

3. Someone who looked like a construction worker and in fact had been, but who had invested every last dime to his family's name in Dell Computers very early on when he worked on their headquarters complex. He figured that any company he hadn't heard of that was building a complex that big had to be going places. He was on his way to stock car races all over the place, in paid F.

4. A chap in a sleeveless T-shirt who turned into a long-term consulting client, ending only when H-P bought the company he worked for.