What is the purpose of the game over screen's score listing?

Edit: As of Beta 1.9, the score displayed on the Game Over screen is the amount of experience that the player has collected throughout that life.

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Old Answer: You cannot currently earn points in Minecraft. Notch intended on adding a points system to Minecraft that would display upon dying, but it was never implemented. However, the placeholder text still shows on the Game Over screen. Perhaps something in the upcoming "Adventure Update" will make use of points.