I always wondered how the Alliance came to dominate the servers when the Horde had more distinctive races. I mean, Horde gets blood eleves, Alliance gets some goofy blue dudes. Horde gets goblins, Alliance gets "Worgen". Who doesn't want to play a goblin?
The factions aren't that terribly unbalanced.
As of 8/26/2010, per
this handy datamining site, Alliance had about 52% of all max-level toons, and Horde about 47%.
Hopefully the guy'll update soon. Maybe in about a month or so after everyone's mains have hit 85, and people who're going to have the new races as their mains will either have changed over* or leveled up. I don't think the overall balance will change, though of course the individual races will likely change (dwarves and trolls, in particular, are likely to go up in numbers).
Now, individual servers can be and often are unbalanced. My server, Malygos, has about a 3-1 Alliance v Horde ratio, which made the open battleground, Lake Wintergrasp, rather unbalanced until Blizzard changed it to a 1-1 entry ratio. PVP servers tend to be fairly even, though if one side gets a significant numbers advantage, that advantage often snowballs pretty quickly.
* - For a fee, you can change a character from one race to another, as long as the new race can be the same class as the old one. For example, I could change my dwarf paladin to a blood elf, human, or draenei, and after the most recent patch, to a tauren. However, I could not turn him into a night elf, worgen, or gnome, since none of those races are allowed to be paladins at this time. Interestingly, while questing, I have noticed a few worgens who'd obviously race-changed, I do not recall seeing any goblins.
Brad