An upcoming patch to the currently-underway Heart of the Swarm beta for StarCraft II will introduce a new feature: player levelling.
Players will earn experience for each race seperately, with points awarded for building and destroying units, as well as for bonus objectives like “bonus XP for your first win of the day” and “extra XP when you play in a party with a Battletag or Real-ID friend”. Blizzard also considering events like “bonus XP weekends”.
What is XP used for? Well, the only currency of value on battle.net, of course: decals and portraits. Higher and higher levels get better and more epic versions, all the way up to level 20. Blizzard warns that XP resets will happen periodically during beta, so don’t get too attached to your current levels.