Create Your Own Fusion Drive
"When Apple introduced Lion, they added a logical volume manager (Core Storage) to the OS. The key factor to Core Storage is that it allows a single volume to span multiple physical disks. Which makes the Fusion drive possible, but it isn’t the only aspect. What turns a Core Storage drive into a Fusion drive is the introduction of automated storage tiering to mix."
These instructions explain step-by-step how to make your own Fusion Drive with OS X 10.8.3. Requirements are, obviously, two internal drives. A SSD and a HDD.