To be clear, the author hasn't been able to use a Fusion Drive on an older Mac. He has instead found a way to create something a lot like a fusion drive by combining a consumer SSD and HD, and getting the OS to treat the combination as a single volume. Most impressively, he also was able to use the SSD "first", moving recently used apps and files to this faster drive.
All the details aren't out yet, so we can't be certain what is or isn't Fusion Drive. However, the speculation is that Fusion drive is more than merely a union of two disks, but with an OS level automatic tiering. (http://arstechnica.com/information-technology/2012/10/apple-...)
Yes, exactly. And citing the source you provide, "This [OS level automatic tiering] is almost certainly done using Apple's Core Storage logical volume manager, introduced in OS X 10.7. As a volume manager, Core Storage has the chops to weld the two separate drives together into a single entity and handle the relocation of files between one tier and the other."
So, then, if you can show that you can merge two disks with CoreStorage, and get it to tier them such that recently used apps and files get moved over to the SSD... what more details do you need?
See also the promoted comment on that ARS page: "First off, I am 100% certain this is HFS+ sitting on top of CoreStorage based on comments made to me by by certain former coworkers who are still at Apple."
Speculation: Perhaps Fusion Drive also is filesystem aware, that way it keeps important system folders, such /Applications and /System and /Users/*/Library, always on the SSD. That way, your OS and apps seem fast, and bulk files such as MOVs and MP3s are on the hard disk.
I used to do this manually when large sized SSDs were past the expense of mere mortals.
