I have discarded many of my computers. I have never thought about the data still left on my discarded computer. I am sure that many other people are like me, orphaning your data in the hands of the recycler. If your data gets into a person who is technically sound and criminally excited, he could make a mince of your data, especially if you happen to have sensitive documents.
Here is a way to permanentally delete your data. There is a feature inside your bios called as low level format. A low level format typically wipes out 99% of all your data. Make sure this is done before you dispose your computer. If low level format is not available, I suggest destroying the hard drive. I don't trust anybody and you shouldn't either. Take a hammer and destroy the hard drive before throwing it away.
If you have further questions regarding disposing a PC, write to me at pcs at suite101 dot com. I would be glad to help you out...