The difference in my experiences was striking. I figured my loneliness grinding away at the lower levels as a troll was symptomatic of being below level 10. As a night elf, I was quickly surprised by how much nicer and more social Alliance players are. I have grouped multiple times, spontaneously united with players to defeat a non-quest monster, and just generally chatted pleasantly. Businesslike calls for groups, trades, and tips were equally balanced by joking around and playful emotes. I am guessing that part of being a hard-core gamer is that all that sociality gets in the way of leveling efficiently and is only really desired when necessary for play.
Someone should do a study. Anyhoo, I know many of my untalkative readers are WoW players. Any comments on Alliance-Horde differences?