Once again, I would really love to see all the statistics Blizzard has as to when and where players play. When a player complains that his realm, Agamaggan, is too low population, Drysc replies that actually, Agamaggan isn't even in the bottom 25 realms. Agamaggan is seeing a 55% nightly population (which means 55% of the realm's normal population is logged on at night), and Drysc says Coilfang (which drops all the way down to a 30% nightly population) could use more help.
He also says that about 200 out of the 225 realms aren't even "hitting capacity" (they've had no queues on them for a month or more), and that most of the realms fall into a "middle area" of population size, where there are enough players to keep up raiding and an economy, but not so many that it's overcrowded. It's also interesting that "overcrowded" isn't actually based on any feelings the players have (at least in this estimation-- who knows what other factors Blizzard examines to keep players happy). Instead, it's all based on the number of players each realm can hold, which was increased in the Burning Crusade. So realms that were "high pop" before BC are actually "middle pop" now-- even if you feel your realm is crowded, as long as they're no queues, Blizzard says things are fine.
And Drysc can even look up the Alliance to Horde ratio on Agamaggan-- it's currently about 1.1:1. Warcraft Realms has a pretty good guess-timation at where realms and numbers are at, but the numbers Blizzard is collecting are probably so accurate they'd make grown statisticians weep. We've gotten small peeks at what they're tracking, but like I said, I'd love to see everything they know about us and our behavior.