I just wonder why they're don't mix both NAND and regular as one huge Hybrid drive.. most of these drives uses large amount of the NAND only as cache, while It's okay and helpful, I guess having the NAND and regular disks works as one big hybrid drive.. imagine 128GB of NAND and one 500GB platter... the OS will prioritize the NAND for demanding files and fast access ( like OS and regular main apps ), and keeps the rest for data files...
almost same concept as Apples new hybrid HDD's in the new MacBooks...