The ability to save replays has turned into a major selling point for Mario Kart 8, as players have had a great time saving their favorite clips of races and uploading them for the respect of their peers. This is the service that gave us the Luigi-stare, and now one player shows just how mean you can get when you're in the lead and hang out onto a single green shell.
This obviously took a bit more time and editing than simply using the built-in tool, but it goes to show you how much fun people have when you give them ways to be creative with the content in the game. Each of these shared videos turns into a commercial for Mario Kart 8 and spreads the word about the game without Nintendo having to do much of anything once the service is built.
These sorts of silly clips are catnip for Monday morning stories (ahem) allowing Nintendo to keep the game in front of potential players for an impressive amount of time.
We live in a culture where our favorite moments from games are moving from the oral tradition into services and features that allow us to tell the tale to a much larger group of players. It's a pretty neat thing, and I'm glad Nintendo is on board.