using Spybot versus formatting and reinstalling everything

[macgig]

I've read that the only way to be 100% certain a system is clean of spyware is to format the drive and reinstall everything from the recovery partition.

Sometimes I wonder if this is the best option for dealing with spyware? the other day I was removing spyware from someones PC and it took 6-7 hours to fully clean this system. After it was done, I was thinking that I could have formatted the drive and reinstalled everything in much less time.

how do you make that decision? using spybot or just zapping the drive and starting from scratch? spybot now searches for nearly 835,000 variants of spyware... on older slower PCs, it takes a long time to run and do its thing. time is money as they say, so I can't help to wonder if a format and reinstall from the backup partition is a better time saving option than using spybot or any spyware removal program?

what do places like staples, best buy, or office depot do? do they run spyware programs, or format and reinstall?

thoughts?