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Never.

Never

Why would I do something that terrible?

Never. I don't understand people who think that format is only way to repair computer...

Never

only if something goes completely wrong.

When I absolutely have to? Which is almost never

Nevar.

Roughly every 18 months to 3 years. I just wait until I notice a significant performance hit that can't be remedied through mere maintenance. I also use it when I have too much sensitive info on my computer and I suspect there has been a security breach.

Never. CCleaner / Autoruns / etc. once a month or so to keep shit from piling up is all it needs.

Formatted mine 4 days ago, just for Try Windows 8 on my computer! Its nice! :P

Almost never

When I have to and there is no other option to repair the computer.

When it's breaking bad.

Only when my system goes kaput.

About once a year ...

Formatted my windows partition twice in the past week, now it runs fine and I have no reason to format it anytime soon... hepefully.

monthly! just the SSD part (OS, Driver, software). just cause i hate updating, i like it fresh
all storage files including STEAM are on my HDD so they dont get affected
google ntfs junction

I only format my machine when I'm doing a massive upgrade. I used to reinstall frequently back in the Windows 9X days, but these days it's not really necessary.

when the world ends.. and maybe i may do it that time

Maybe once a year.

Whenever a new Windows version releases and has better stability.I'm using Win7 right now, I'll format when 8.1 is out.

With ALL the work I have in .psd format inside this HDD (they take almost as much as my games!)?!

Never, thinking about it just gives me the creeps.