On my server I was surprised to discover that warlocks were less frequently played than priests. However, it seems that the landscape is changing as everyone and their mother has made a priest alt. Druid remains at around 3% of the population. Hunter, paladin, and rogue are the most populous alliance classes by far on my server. However, for hunter you have to divide up the numbers because I swear at least half the hunters I have met melee with their pet tanking and only shoot to pull.
Oh and I suppose the same is true for paladins. You must divide their numbers up because half the paladins never cast any spells beyond seals.
As for race, huge number of humans and night elves, some dwarves and very few gnomes.