Nostalrius (from what we've seen so far):
A very populated server (-7000+ players in prime time), cca 50-50 Alliance vs Horde (
http://forum.nostalrius.org/viewtopic.php?f=6&t=3641&hilit=horde+ratio&start=150#p112079), sometimes lags due to that many players but I think its better to have them all because its very easy to do things like elite quests, dungeons, etc (especially in prime time).
Mentality of players - Horde is much more helpful in world pvp on all levels but they're also the scum of Azeroth, always looking for an easy kill (waxing lower levels, ganking 2:1, etc, they even kill you right after you've helped them), while Alliance players just walk by you and watch you getting hammered and do nothing.....for that reason some Alliance players quit and re-roll Horde to join the nerdwave. Stranglethorn Vale, for example, is very hard for Allies to quest as Horde has a base with flight path in the middle of the map and they gank you all the time so having company during questing is a huge advantage, the 3 of us just kill everything that moves while on the run and it goes quite smooth. Soloing is much tougher. Horde is renown for lvl 60 no-life imbeciles who just pick an area to harass low level Allies that quest there. Also - when you kill a similar level horde player during your questing they often logout and come back with their lvl 60 main to haunt you, thats how pathetic they are.
Our main goal is to have some fun in all forms of pvp when we hit 60, hopefully we'll be able to get that. If not - well leveling is quite fun after all that time, especially in a group. All in all - World of Warcraft as it should've remained, much better than that crappy retail filled with robocops, aliens and transformers.