MacRumors reports developer Patrick Stein's successful experiment to create a Fusion Drive on an older Mac Pro. It looks like all we need is an updated Disk Utility to make this easy for anyone to do. Anyone with both an SSD and an HDD installed, that is!
Fusion Drive is a just-announced Apple technology that binds an SSD and a traditional hard drive into a single volume, and moves application and data files to the SSD for faster access as needed. It was announced last week as a build-to-order option on the new iMacs.
Hit the link for an overview, or drill down to Stein's Tumblr blog for the nitty-gritty details.