It's IPv6 launch day.
In February 2011, the Internet Assigned Numbers Authority (IANA) ran out of addresses to allocate to the Regional Internet Registries. While some of your devices may already share a single address (your home router acts like a switchboard for your home's devices), if IPv6 isn't implemented you'd soon have to share a single address with multiple people or even a whole neighborhood. This tangled, constrained Internet would be unsafe and unsustainable.