Deleted

as often as i fap

Never, except the C drive when I have to reinstall windows.

Once in january and once in june

Whenever I install a new Linux distro I reformat which partition I install it on.

I nuke my OS and do a fresh install twice a year.

When the need arises. Ergo hardly ever.

every month

Lolz?
Last time I did this is when I installed Windows 7, meaning when it first arrived on MSDN - September/October 2009 :)))

I almost never format my own computer, the exception being the times when I need to set up a new partition. However, I do format drives pretty often.

I work in tech support.

Every 2-4 months normally, only really because I like the feeling of a fresh start.
I actually enjoy setting everything up once again.

Never. Really, never did that with any of my computers, I know how to keep them clean.

I'm surprised by amount of people who use ready made systems or can use unformated discs ;D

Not often, only really to change windows OS's. in the case of Linux I reinstall Linux all the time, since i like playing with it and just reinstalling to get rid of the rubbish (its faster)

I used to do it much more frequently but Windows has gotten much better in that regard since XP. It's usually easier to just maintain my machine now than it used to be and I rarely need to reformat. I have a couple small bugs that have crept into my system that I can't resolve but they're not large enough yet for me to bother doing a full reformat.

when a mysterious virus out of nowhere beats me

My last format is more thank a year and half away.I like to keep my pc fresh and light.
Also diskeeper helps immensely to keep the hdd fast and efficient.

Only if I'm building a new PC, or if something happens to my install to the point where there is no other option.

I used to format it around twice a year, but lately it has a long time that i dont do it, i think two years without format