With an upcoming patch for the Heart of the Swarm beta, Blizzard is going to introduce a new race leveling mechanic in StarCraft II. Mastering a race will give reward players with new decals and portraits to show off just how good they are.
Each of StarCraft II's three races will each have a separate leveling bar; playing in either Blizzard matchmaking or custom games on Blizzard maps will get you XP for either Terran, Protoss, or Zerg depending on which race you're controlling. Crushing your opponent will net you some big rewards and the developer is looking at XP rewards for things like getting your first win of the day.
Leveling up your races will net you the aforementioned portraits and decals, but you'll also get a ranking next to your player portrait. I imagine this is going to to be a great psychological tool against players; seeing a lvl 20 Zerg player would put the fear in me for sure.