I like the unexpected encounters. A bird joining my circles, turning its head and probably wondering about this drunken sailor...before zipping off to a better place. Crossing lines with a solitary seagull while cruising down the coastal ridge. Chasing it a little until it, too, shows me who's really at home up here. A sailplane drawing concentric circles together with me...and I catch a glance of the pilot in his fishbowl.
Racing along a track with others during a competition is great, but even better is flying cross country together with a buddy, branching out to snoop for lift.
My favorite encounter was on a flight in the Bavarian Alps. At the launch I met an real nice HG girl, and it was just the two of us on that mountain. We set up, said our "Have a good flight!" and flew off. I went for a short O&R and when I came back she was circling over one of the ridges. I joined her and together we played almost until dusk. After landing we shared a beer...and I never saw her again (perhaps she's reading this here? )