I changed the hard disk in my Netbook with a Seagate 250GB hybrid, mirroring the content over using dd_resecue in Linux. After the first two boots of the change-over, the start-up time has halved and is more responsive even with multiple applications open. It's certainly a heck of a lot better than any improvement I managed to get with "ReadyBoost". While applications load up much quicker, it's not instant opening like my desktop's OCZ SSD, but quick enough that makes the upgrade well worth while. I noticed the upgrade the most during my recent vacation, as it came out of hibernate to on the web much quicker.
While hybrids are likely to become popular over the next few years, I would imagine that spinning hard disks will become obsolete once NAND flash or some other form of solid state storage eventually catches up on pricing.
As for failing hard drives, from my experience, hard drives that fail seem to vary from manufacturer to manufacturer each year. For example, up until 2008, I haven't seen any WD hard drives fail and lately seen plenty of 2.5" Scorpio Blue failures and two recent Caviar Blue failures, one which I helped someone replace this week and the other being a new drive I bought that failed two hours after installation. Seagates and Maxtors were the two most common brands I use to see fail, but haven't encountered any recent failures of these brands.
Regardless of what brand of hard drive one uses, always keep a backup, even if on another hard disk. For my own hard drives, I have had 4 failures since 2003, all different brands - one Maxtor OneTouch external 3.5" 250GB (5 years ago), one Samsung Spinpoint 2.5" 120GB (3 years ago), a WD 3.5" Caviar Blue 250GB (1 year ago) and an OCZ Agility 2.5" 60GB SSD (4 months ago). The three hard disks failed by collecting bad sectors, although I've seen HDDs totally fail (e.g. not spin up, not show up in BIOS, etc.) and two were replaced under warranty. The SSD totally failed unexpectedly, I left the PC and came back to see a boot disk failure message. I got this replaced under warranty and restored a backup. In all cases, with the help of backups, I didn't lose any information.