In most Xbox 360 games, unlocking an achievement serves no other purpose than to boost your ego a bit and give you bragging rights. Occasionally you might also unlock some artwork, gamerpics or videos, but rarely do you gain something useful with your hard work. Universe at War will reward those that put in the time to unlock multiplayer achievements. Not only will you get some points, you'll also unlock a medal that can be used in multiplayer matches to give you an in-game bonus. IGN have the full list of achievements, including what medals and bonuses you'll unlock for completing multiplayer objectives.