Format is too risky, there are ton of tools outthere than can recover data from HD even after they have been formatted.
If you have sensitive/personal/private information. When a HD fails/gets replaced.
1) Physically destroy HD (Drill a few holes on the HD)
2) use software (as mentioned)
Even if the HD fails just because you cannot fix it, it does not meant that it cannot be fixed.
Probably paranoid, but I had to do this to 20 company computer before donating them to goodwill.
http://www.ontrack.com/We've used Ontrack in the past to recover HD RAID partions after a repartion and format and they recovered 100%.
(Sys admin added additional HD to server , was asked if he wanted to add to existing raid he said yes , repartioned and reformatted. before realizing what he was doing)