Blocksworld Premium is the the first pack that costs real money. The second pack that costs real money is Animated Blocksters. What's special about it is that all the blocks it contains are coming in INFINITE quantity, which explains the $7,99 USD price tag.
This pack now contains around 183 pieces. This number will increase each month along with newly released action blocks.
For now, the pack contains ALL the building blocks that are in the "Blocks" section, ALL the action blocks (new ones are added each month), most of the "Decoration" blocks and many textures and sounds. As of now, a player owning premium will have the navy blue and gold texture on their interface and worlds.