When I moved across the US a year ago, I had a ton of older hardware and less room to move into (house to apartment). Basically, I gave everything away that I wasn't actively using.
Rather than muck about with secure erasing or degaussers, I just took the dozen drives out to the shed and beat the daylights out of them. Most of my machines were in various states of not running--so the amount of time I would have had to spend putting together a working machine, swapping around more than a dozen older drives, running secure erase on them ... well, it just seemed a lot simpler. There was no way I was giving intact hard drives to random people I did not know, especially drives that may or may not have been erased enough.
I recommend safety goggles. Some of the boards tend to shatter and send little bits flying everywhere :-)
Could some super spy possibly lift data? Maybe. But no ID theft script kiddie will. I saw it like using a paper shredder--only a lot more fun. Sure, some super spy agency might be able to re-assemble shredded documents or lift data from the mangled platters of my drives--but why should I be worried about them? They already have a current file on me, I'm sure--they don't need old drives ;-)
A friend of mine put it nicely: "There's nothing like the feeling of raw destruction you can wreak with a 10lb sledgehammer." It's right up there with using a proper chainsaw. Deconstructing stuff is *fun* :-D
If I am ever worried about super-spies, I look forward to discovering the wonderful destructive power of thermite :-)