I've been following this thread with interest.
I have never had a drive fail, although I pulled a 8Gb HDD from my Beige G3 when it started ticking. How long ago was that!?
Anyway, I downloaded DriveDx and ran the trial. I buy HDDs for data and SSDs for OS/apps. I tend to replace a drive at the end of its warranty period and move it into a backup role.
DriveDx reported the SSD I use very rarely for Snow Leopard at 35% of its lifespan. As it's over five years old, that's not surprising. But what did surprise me is that the 80Gb IBM SSD that I keep on the shelf as backup for the SL drive was reported as excellent over the USB connection and it is over eight years old! I guess it is lasting longer because it is not powered up all day?
Anyway, it cost me £40 today for a DriveDx license and a new Crucial 120 Gb SSD.
Cheers!