ExtremeTech reports hybrid hard drives are dead because Microsoft isn't backing the technology in Windows 7. Hybrid hard drives are basically HDDs with some flash memory as cache, this was supposed to improve performance and battery life, but it didn't work as well as expected. Microsoft was supposed to make some adjustments in Windows to better support hybrid HDDs, but it doesn't looks like the software giant isn't interested in supporting the technology.
Hybrid hard drives, as you may know, merge the solid-state-disc (SSD) and the rotating hard drive together, with a bit of flash serving as a cache. In concept, it's not a bad idea: while the performance gains have been on the order of 10 percent or more, the real bonus was supposed to be in the battery life, which would reduce the need to spin the disk, and "squirt" the data to the disk in one big spurt once the flash cache was full.
In reality, however, the first hybrid hard drives required even more power than a conventional drive, to power both the flash memory as well as rotate the disk.