Out of that grand total I have personally contributed a little over 50,000 coins. I made a nice little contribution to the total, but my goal is to hit one million since the official site for the game says players are awarded something special when they collect all those coins on their own. Don't you want to know what is awarded? Well right now that is a mystery to me and obviously a few others, but I do know one little secret.
There is more than one playable character in New Super Mario Bros 2. Yes it is true you can play the game as Luigi himself. Requirement number 1 is you have to complete the game at least once with Mario. That means you have to defeat Bowser on World 6. Once you have completed that challenge you head on over to the solo play choose a file screen on the main menu. When you get there, hover over the file that you completed and while holding down the L and R buttons you select the file with the A button. Finally you can play as Luigi.
Hope you enjoy playing as him. Maybe you will find some more secret areas in the game, little tunnels here and there, a secret plant to climb yourself into the sky. Here's one more secret: there's a hidden section near the third coin World 1-Level 1.
How many coins have you accumulated in the game? Have you gotten more coins than me, tried coin rush mode yet, played the co-op with a friend? If the answers any of these questions is no, there is only one thing to do. Go and play some more New Super Mario Bros 2.