Stolen from MK8 Staff's Miiverse post:

"[IMPORTANT NOTICE] From now on, you can know who is playing Mario Kart 8 now through smart phone or PC. Lots of features to enjoy Mario Kart 8 more which include watching every tournament's movie and checking not only yourselves, but everyone score and movie too! Please come to peek once!"

I checked it briefly and it lets you see current highlight reels and checks if you're friends are online when you go to your friend list. Has anyone else use this website and discovered any more stuff on it?