I just returned a laptop as part of our refresh cycle and decided to 0 out the drive using Linux before shipping it. I tend to store a lot of customer data and I have no idea where the machine will go once it leaves my hands. I know my process was not the most secure possible since I predictably just wrote a blank volume over the disk 7 or 8 times using a method I found on CNet. Today I saw a post on ZDNet that looks like a much better solution.
Another interesting thought - if you had BitLocker enabled on your drive throughout it's life and you required either a USB key (startup key) or PIN number and now you are decommissioning, you are taking an additional step to protect the data. It was encrypted (AES 128 or 256, you decide) during it's life and if someone is trying to decrypt it after recovery they do not have the certificates needed, assuming you cleared the TPM or used a startup key so the cert was never stored locally.
This is of interest to many of the people I work with in the field who donate computer lab machines to local school districts at the end of a hardware lifecycle.