One of the things I enjoy the most about this game is the fact that I don't really have to play with anyone else to enjoy myself.
Sure, there's people around, and generally when I'm questing there's someone else around in the area, maybe even working on the same quests. But even though they're there, I don't HAVE to join with them if I don't want to, because the world is huge, especially with a family of 5 actively-played alts.
On occasion in my questing, I run across Alliance players instead of Hordies. Nowadays it's not so easy to tell an Alliance from a Horde on a PvE realm (our names are all in blue for the most part) because the darn Blood Elves look so Alliance-y they've messed up my entire interpretation of Alliance vs Horde. About 2/3 of the time, that Alliance player turns on the "enemy" switch and starts doing things like hogging mobs, tapping nodes I'm battling a nearby mob to tap, and even training a long line of mobs onto me.
About 1/3 of the time, however, I get into a "friendly" situation with an Alliance player, where I assist them when they're fighting and get an extra mob aggro'd, or where they wait politely for me to choose and attack my target before selecting and attacking their own.
The other night I had a favorable experience with a level 50 Alliance Night Elf Druid who was playing in the same area I was in Un'Goro Crater, where we progressed into the Hive tunnel together, taking turns on the mobs and putting in a few hits on the others' mob on the way through, just to make it easier for each other.
Occasionally we'd seperate and go our own way. One time when I came back down the tunnel towards him and joined into the fight, I saw he was actually fighting two of the 52/53s, and although I didn't check the Alliance player's health, my jumping in probably saved his fur at that time. He thanked me, and I /cheered him ("Power to the Forsaken!").
We progressed into the main egg room, which had a Rare spawn in it. Alliance pulled a mob, and we took it down. Then he stealthed and snuck into the room and tried to take down another non-rare mob that was in the room, and the Rare aggro'd, so I charged in on the Rare to get his attention, slapped on my shield and went into Defensive mode, and turned my attention to the non-Rare that had initially been attacked from steath.
Unfortunately, the Rare spawned egg-buddies that eventually downed us both. Alliance guy died first, and I died about 5 seconds afterwards.
I almost created an Alliance toon just to log in with and thank that guy for the fun shared play, but let him know I was going to rez at the Spirit Healer because it was time for bed.
Unfortunately, I forget his name. Next time I'll take note, and maybe I'll post something friendly on the Official Forums for Zul'jin.