No matter what everyone is saying, IPv4 is still widely used in internal networks. Just look at any home wireless router these days. Just about none of them come pre-configured for IPv6. The same goes for most businesses. Unless you are a giant corporation, or you run an ISP company, the demand for IPv6 for the internal network hasn't grown all that much. At least, not from what I've seen.
That being said, the ability to know subnetting, and carve out IPv4 networks is still a valuable skill to know. Sure, there are subnet calculators available, but sometimes having a quick reference chart available that you can tack to your cubicle wall is more handy.
So, I give you my subnetting reference chart!
Feel free to print it out, share it with your friends, or use it for your next certification exam!