Lately I've been told of 2.5" hard drives, in laptops, crashing; but I've never really experienced a true hard drive crash in 30 years of computing. I have one now, because a power surge in a desktop corrupted my Mac memory, which corrupted the file system. A $40 line conditioner would have eliminated the power spike, and daily backups (and good partitioning, /User) will repair it. Soon I hope to add a larger, second PATA drive and mirror the /Usr partition.
Ironically, this was less likely to occur in my 1984 IBM PC, whose memory had a 9th parity bit for every 8 bits. (In those days I used SpinRite, and I'm pleased to read it's still doing well.) There are free, TSR programs that check your disk regularly and log, mail, or (in Windows) toss up a warning if things seem bad. (I should be more comfortable comparing two logs.)
My machine is for scientific computing: I repeat all important computations. Servers and desktop machines (formerly workstations, like Suns), for those who cannot afford the time to do this, should have ECC memory (with an extra bit per byte), which takes very little extra time & money. However, it's available today only on professional servers, workstations, 2009 Power Pro Macs of great speed, and no doubt some expensive Windows machines. If you're a physicist post-processing supercomputer data, or just an actuary, you might need one of these. Memory in the future will likely count errors to predict upcoming problems with a memory bank.
An online book I've found useful is 'Minimizing Hard Disk Drive Failure & Data Loss', online at: http://en.wikibooks.org/wiki/Minimizing%5Fhard%5Fdisk%5Fdrive%5Ffailure%5Fand%5Fdata%5Floss
Hard drives, ATA & SCSI, for about 15 years now, have used S.M.A.R.T. to predict upcoming drive failure. Though different companies use different criteria to throw up a warning window, the meaning of many of S.M.A.R.T.'s numerous measurements are clearly given in the Wikipedia article on it. You needn't rely upon your software company to calculate a single number, like an IQ. :-) Check the red sections of en.wikipedia.org/wiki/S.M.A.R.T.#Known_ATA_S.M.A.R.T._attributes
Those who can use a command line can measure these attributes using a free package from Sourceforge called 'smartmontools'. (The Windows version pops up a window.) Find it at sourceforge.net/apps/trac/smartmontools/wiki/TocDoc
Try /usr/local/sbin/smartctl -i /dev/hda, or
try /usr/local/sbin/smartctl -i /dev/sda for SATA drives on Windows.
All the numbers it gives can be evaluated by examining the above Wikipedia page. Also provided is a resident program that tests the drive every now & then for slow degradation. If you wish to tune your drive (for faster speed or) to make it slower, quieter, & more reliable, you can also try setting the hard drive parameters with 'hdparm', found at sourceforge.net/projects/hdparm/
I haven't the Windows documentation, but on Debian Linux I use:
/sbin/hdparm -i /dev/hda
for my PATA drive, just for information (and information on secure deletes). Thus far, I've left the default settings alone.