The latest update being pushed out to StarCraft 2 "Starter Edition" in the US brings the game version 2.1. This new update unlocks three races: Terrans, Zerg and Protoss, as well as providing custom maps.
The custom maps can be accessed through the Blizzard Arcade, which is a free game-hosting platform and editing suite offered by Blizzard. This means that if someone posts a new map for DOTA, Warcraft 3, or even StarCraft, everyone in the world will see it, not just StarCraft 2 owners. The US is first with the patch, but it will roll out to other territories shortly.