It is being called a multitude of things: the Powers of Ten Day, Eames Day, 42 Day, etc. Some are just calling it 10/10/10 day, or Ten Ten Ten day.
It's one of those calendar oddities that no one really know how to explain, but for some reason, we're all fascinated by it.
It's probably because 10/10/10 will never happen again during the lifetime...