Macworld magazine tests the late 2012 Mac Mini:
But it was the Fusion Drive that really kicked the BTO Mac mini into overdrive. The standard configuration $799 Mac mini with its 5400-rpm hard drive took more than three times as long to complete our copy file and uncompress file tests as the Fusion Drive did in the BTO Mac mini.
Data is written to the SSD first, so the idea is that you get SSD speeds but with the capacity of standard hard drives. As you can see, our benchmark tests bear that out.
The tests involve duplicating a 2GB folder and also compressing and uncompressing a 6GB folder. In short, perhaps ~20GB of data at most on a Fusion system (amount depends on whether all copies were kept around). Since a system with lots of applications might total 40GB or so, the hard drive would never even be touched. 20 + 40 = 60. Since the SSD component is 120GB, MacWorld is not testing anything but the SSD performance on an nearly empty drive (~60GB on a 1,120GB volume of 1,000GB hard drive + 120GB SSD).
This is like testing a car for gas mileage by driving it down a 10% grade to the bottom of the hill.
With less then 120GB stored, the tests are running entirely on the SSD. If one is to promulgate such grossly misleading tests, there should be a prominent advistory caveat which accompanies the test.