There have been more than one occaision where I have upgraded an older machine with a hybrid and found the experience to be slightly improved over regular spindle-only hard drives. My experience has been that older chipsets don't allow the full experience of SSDs to come through due to other bottlenecks and SSDs have a long way to go before big volume is affordable. Hybrids fill this market niche nicely - nice balance of performance over volume at a reasonable price point.
Certainly, I use hybrids exclusively now and I have bought about 3 or 4 over the last few years. I have noticed no errors or failure rates above spindle-only drives and they appear to make the user interface a bit 'snappier'.