How do you stress-test your Hard Drives?

Current Mean Time Between Failures(MTBF) for consumer SATA drives is 10^14 write bits. This means that if you have a 2TB drive and write every bit 50 times on the drive, and then try to read every bit, you will have a disk failure in that time.
Google has done a lot of statistical analysis of consumer disks and have noted several trends, the most important to your question is that you will get about a 10% chance of failure in the first 3 months if you put your disk in high-utilization (stress test). If it makes it past the first 3-6 months, then it will last 3-4 years before the failure rates starts going back up again.
It's interesting reading if you like statistics, and even those of us who don't, still get the idea from the graphs...
Google link
Another source is Carnegie Mellon

EDIT: One other thing that relates to your question from the Google paper, is that these rates apply across all drive manufacturers. Google buys whatever gives them the most MB for the buck.

I don't stress test them at all but I do keep an eye on SMART values. I use Speedfan or HDtune to view the smart data.