When you're on the side of the Alliance on a PvP server, MOST of the time you have to fight Horde who either don't like you, or just want some Honor Points. (Not to say that the Alliance doesn't do it either!)
But one day, in Stranglethorn Vale, something VERY different happened. I came face to face with a very high level Horde who was being attacked by guards. Once she had finished off the pathetic guards, she walked over to me with her level 60 mount, greeted me with a friendly emote, and beckoned me to follow her with another.
So, being the curious cat that I am, I followed her, and to my surprise, she had tracked down Sin' Dal, the powerful Stranglethorn Tiger. (Now of course she was a hunter, so that gave her an advantage...) So, with an emote that said "Charge!" I made the first blow on the tiger and together we made quite the team, despite the fact that she was doing most of the work.
After the battle was over we said our goodbyes and left. I turned in my Tiger Mastery quest, and hoped I would meet that same blood elf hunter again (and also hope that she remembers me!)
Things like this just go to show, that whether black or white, red or blue, Alliance or Horde, you can ALWAYS make friends.