Considering that defragmenting hasn't been necessary for probably well over a decade, I would suspect you have something else going on. Wouldn't surprise me if the drive is on its way out.
In the meantime, the choice is ultimately yours whether you continue to prove PT Barnum right when he said that there's a sucker born every minute.
I have a mini-mac with OS10.6.3 and I have to de-frag files every week with Tech-pro. It takes an hour to do so. I never had this problem with my other macs. The machine slows down and acts weird until I do the de-frag. I run a virus program and the machine is clean.

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