Realms in World of Warcraft are supposed to be like different, although identical, worlds. You choose one and live under its rules, and if you want to live in a different world, you have to put in a lot of work to get there. But quick glance at the WoW Realm Forums shows that each server might better be described as its own little high school.
Realms have nicknames, whether they be good ("TichOWNdrius") or bad ("Argent Down," "Lagging Skull.") They have celebrities both famous for their exploits (Death and Taxes on Korgath, Sebudai on Doomhammer) or infamous for screwing up (Overrated on Black Dragonflight, Avatar on many servers but originally Warsong.) They have private dramas and screrenshots that will be funny only to residents of that realm.
Servers are known for different things: Argent Dawn has good roleplaying (and entertaining Goldshire cyber stories), Mal'Ganis has innovative world PvP, and Black Dragonflight and Korgath have some top raiding guilds. Some servers have rivalries -- Arthas and Mal'Ganis have been sniping at each other about server population since transfers opened up, denizens of Blackrock regularly invade RP servers when Blackrock itself goes down, and informal competitions develop within battlegroups. And a couple servers even have official mottoes. The two I can remember right now is "Tichondrius is not for you" and "Mal'Ganis KICKS!"
My server, Magtheridon, was released shortly after launch. Our only celebrity is Xzin, we don't have any earth-shattering guilds, and we're not the best at PvP. People talk a lot about the "Magtheridon way," which as far as I can tell involves Alliance outnumbering Horde and liberal use of the server's unofficial motto, which is three words long, begins with "go" and ends with "yourself." Still, it's a nice place in spite of the lag, and I wouldn't want to transfer anywhere else.
What's the culture of your server? Is it populated or quiet, dramalicious or kind, vicious to outsiders or welcoming to new players?