Interestingly, World of Warcraft's primary player vs. player gameplay in battlefields will also be based on quests. That is, although battlefields are instanced (they're loaded up as areas that are separate from the main gameworld), they won't simply be a place where two huge mobs of players collide. Instead, they'll be the site of a series of quests that culminates in an eventual team-based goal. For example, the primary goal of Alterac Valley (and likely that of other, future battlegrounds) is to hunt down and destroy a computer-controlled commander character who belongs to the opposite faction. However, you can't make this character appear unless you complete a series of ancillary quests on the battlefield first. The game will use a faction-wide broadcast system to inform you of when each of your side's quests has been completed. If you can complete your faction's mission first, and limit your player vs. player skirmishes to enemies of about the same relative strength as you, you'll earn "honor," a new distinction that was added to the game at the very end of its beta test.
Players that got the game last night said battlegrounds are not in, yet. But it might be simply that they're not available to lower levels, yet. That's not certain, however. We'll see.