The user group for the products of the company I work for had an amusing thread a while back about good methods for destroying old backup tapes from servers.
Among my favorite suggestions:
– Put them on the magnetic security desensitizer and bang them several times
– Microwave DVDs/CDs "Smells bad, but a good light show"
– Give them to your medical professional spouse to run them through an MRI scanner
But the hands down winner?
"The tape itself is great for tying plants to supports stakes in the garden. The old 1/2" stuff was best, 2400′ would handle a lot of tomatoes, but 1/4" should still do."