I ALWAYS try and say hello/goodbye/thanks, regardless of who's aircraft I'm on, jumpseating or otherwise. You never know when that guy or gal up front might be able to help you get a job, a ride, or anything else. I guess like everything else, friendliness/being courteous is on the way out. This industry is way too small to be a jerk. Geez............... And oh, BTW, I ALWAYS have time to talk to a fellow pilot/aviator if they want to stick their head in the cockpit to say hello. The conversation may be short, but saying hello and welcome aboard doesn't take THAT long. It's always nice to know there's experience in the back if you need it.