April 20 isn't just a holiday for stoners: In a world where recreational marijuana is legal in eight states, it's basically the entire Christmas shopping season rolled into a single day for pot businesses. "We're just expecting to get slammed," the owner of a smoking room in Colorado tells CNN. One expert expects to see an increase in business of 30% to 40%, especially as some marijuana retailers are offering discounts of up to 50%. It's no wonder Thursday is being called a "really good time to stock up" for potheads. Here's what else you need to know about 4/20: