Sean7432,
Amadis of Gaul pretty much summed it up at the day-to-day level. I would add that the bigger the airline the more anonymous one can be. This is mostly good.
At one major US carrier with 14,000 pilots, for example, one airplane in one base has 500 captains and 500 FOs (you math majors can calculate how many possible 2-person combos can be made from that). They have a preferential bidding system where each pilot bids for his own schedule from a huge pot of trips vs bidding for preset schedules covering an entire month. When you factor in people going on vacation, training, sick out, contractual provisions to drop/swap trips it's possible to fly a trip with someone and, with no exaggeration, never even see that person so much as walk through your field of vision...ever again in your life.
They have many bases...some smaller than others.
Forget the flight attendants. Interacting with them socially on a layover is mostly a nonstarter. There are 23,000 of them and their scheduling parameters are different enough that you'll also rarely if ever see them again either: you lay over...they don't. They layover...you don't.
Small airlines will be a bit different.
If you're a mil guy, you've got buddies at the airlines who can give you more of the inside scoop at more than one carrier.