A good amount more information has surfaced over at Ars Technica about Apple's new Fusion Drive.
Everything I read in this article sounds like good news. I no longer think there is a particular risk when using the technology, so long as I'm backed up regularly. I'm always backed up regularly, and you should be, too.
I'm surprised that it's possible to hook up external USB or Thunderbolt drives to your Mac and use them combined with an internal drive, as a Fusion Drive. But it's cool that it's possible. This may enable people with older Macs to benefit from the technology.
Furthermore, Fusion Drive works at the block level of the disks, below the file level. This essentially means that if you have a huge file of some kind but only want to regularly access a small part of it, the small part will be moved over to the SSD, but the rest will remain on the regular hard drive. Awesome.
It seems Apple has surprised us again; just like the A6 chip in the iPhone 5, a lot more work has gone into Fusion Drive than we (or at least I) initially assumed. Great stuff.