More of this old canard!
After a secure erase with something like Boot and Nuke/DBAN recovery of anything other than the occasional disjointed scrap is impossible even with sophisticated, time-consuming and expensive data forensics.
This may just be enough if crims/police are targeting a company or an individual, but the idea that when Smith, Jones or Brown chucks an old hard drive that some one in the junkyard is going to spend time and money running forensics on your old HDD is just plain silly.
Yes, you should do a secure erase but more than that is just over-paranoid and silly.
Mac
[Actually, if you're sure you'll never use that old 4GB drive then it's more fun to dismantle it and play with the magnets, and a lot quicker just to run a drill through it.]