That depends on how you dispose of old hard drives and computers. If you run Windows, Microsoft recommends cleaning the hard drive with the secure delete command-line application, sdelete. Whatever operating system you run, you may prefer to Use an Ubuntu Live CD to securely wipe your PC's hard drive.
The Frontline video, Ghana: Digital Dumping Ground not only exposes the human health and environmental costs of disposing of computers, but about 8 minutes in, shows data recovery on those same computers that should make the hair on the back of your neck stand up.
One of the reasons I got into computer programming is that it eliminates paper, saves trees, and eliminates paper waste. Electronic devices require electricity, but more importantly, they break or become obsolete very quickly and we replace them. The impact of our obsession with newer, faster computers and other electronics is astounding. But even if we think we are recycling, we might be creating new waste problems in far-away lands as the 60 Minutes Electronic Wasteland video shows (also shows data recovery).
Anyone who reads this blog knows that when my computer became unacceptably slow running Microsoft Windows XP about 9 months ago and I switched to Ubuntu Linux and have been delighted with that decision. File operations that took hours on Windows take minutes on Linux. Everything else seems to run about twice as fast. So if you care about the impact of disposing of your computer (of if you want to save money), install Linux and keep your hardware twice as long. My laptop was bought in 1999 and I run Xubuntu on it (a lightweight version of Ubuntu). It's great for email and web browsing and with a little patience, I can even run a database and a web server on it, even though it only has 500MB memory a 500Ghz processor, and an incredibly slow disk drive.
Thanks to my occasional involvement with UCLUG, I learned of Free Linux PC. They are a fantastic organization that takes donations of old computers, installs Linux on them, and gives them to people who don't have a computer! I've given them a laptop and some memory and I've volunteered at a giveaway at the Greenville Public Library which was a great time. The recipients were pinching themselves.
Here's an old-fashioned recipe for improving environmental, human, and security impacts of your computer usage:
ReduceBuy new computers (cell phones, TVs, etc) less often. Use your old ones longer.
ReuseInstalling Linux can double the useful life of a Windows computer. If that's not for you, then donate any still-working equipment to FreeLinuxPC and they will do it for you.
RecycleRecycling sometimes works and is probably better than burning your computer on your front lawn (though it might still be burned in Ghana, Taiwan, or China), certainly better than throwing it in the trash. Even if you don't recycle, if you can find recycled gold watches or other products made from recycled computers, you are supporting an industry that badly needs encouragement.
In any case, make sure to wipe the hard drive before disposing of it!