I'm probably about once per year on my workstation at home. I used to be more frequent, but I've become far more discriminatory on what I will install that the machine doesn't get too messy any more...thus less need to clean up.
My Computer
Computer Manufacturer/Model Number
Self-Built in July 2009
OS
Windows 7 Ultimate x64
CPU
Intel Q9550 2.83Ghz OC'd to 3.40Ghz
Motherboard
Gigabyte GA-EP45-UD3R rev. 1.1, F12 BIOS
Memory
8GB G.Skill PI DDR2-800, 4-4-4-12 timings
Graphics Card(s)
EVGA 1280MB Nvidia GeForce GTX570
Sound Card
Realtek ALC899A 8 channel onboard audio
Monitor(s) Displays
23" Acer x233H
Screen Resolution
1920x1080
Hard Drives
Intel X25-M 80GB Gen 2 SSD
Western Digital 1TB Caviar Black, 32MB cache. WD1001FALS
PSU
Corsair 620HX modular
Case
Antec P182
Cooling
stock
Keyboard
ABS M1 Mechanical
Mouse
Logitech G9 Laser Mouse
Internet Speed
15/2 cable modem
Other Info
Windows and Linux enthusiast. Logitech G35 Headset.
Since Windows 98, once. The reason was to install Windows 7. Unless there is a very serious problem, I do not think it is warranted to reinstall. Just maintain the computer properly.
i do it every 6 month. this is what i recommend for everyone. though with 7 i might have to change this. 7 does not seem to get bogged down like vista and prior with leftovers from installs and uninstalls.
Back in my pre windows 7 days and before helpful forums like this I would be reinstalling my OS every 2 or 3 months either some major system app like widows media center quit working properly or I Couldn't use system restore to fix my problem of the day I would have to do a recovery taking 3 more days to reinstall everything (single OS). Since Windows 7 I have learned the value of using an image to back up both OS. Using triple protection such as windows image backup, Acronis True Image WD Edition after having to buy another USB External hard drive & throw in Paragon backup & recovery for good measure reduces a week and half's work to about 3 hours
I just make sure everything works before I make a new Image and a bonus of making more than one image is I can go backward in time if I am not happy with my current setup or if one of the 3 backups doesn't work plus I do not need to reactivate widows or other software that may require activation or only allow limited activations as they were already activated before the image was created.
Onboard Realtek or Nvidia High Definition Audio (HDMI)
Monitor(s) Displays
Samsung JS7000 50" SUHD TV or Samsung 27" FHD 60Hz 8ms GTG V
Screen Resolution
1920 x 1080
Hard Drives
1 x Samsung 870 EVO 250 GB SSD (Windows 10 Pro), 1 x Samsung 850 EVO 250 GB SSD (Windows 10 Pro)
PSU
Corsair AX860 - 860W Modular Power Supply
Case
Phanteks Enthoo Luxe Full Tower Case - Black
Cooling
CORSAIR Hydro Series H150i PRO RGB 360mm Liquid CPU Cooler
Keyboard
Logitech K830 Illuminated Living-Room Keyboard
Mouse
Logitech MX Anywhere 2S Wireless Mouse
Internet Speed
100 Mbps
Antivirus
ESET Internet Security
Browser
Latest Version Of Firefox & Microsoft Edge Chromium Stable
Other Info
LG Super Multi Blue Internal Blu-ray Disk Rewriter - BH10LS30
6x2 HDMI Switcher (6 inputs, 2 outputs) so I can send the output of my Cable Box, Roku, or any my 4 computers to either my TV or Monitor separately or simultaneously.
not to often if i can help it although saying that i had a problem with the code 5 error on my daughters desktop and installed from within windows and it was practically unuseable so i did a reinstall this morning on it using the "ultimate boot cd" to boot into the windows disk and its fine now.
and i finally recieved an upgrade disc for my other daughters laptop and im installing it now,so that will be 2 desktops and 2 laptops running windows 7 one ancient acer running ubuntu and one laptop with vista still on it (cant do that one charger is knackered need a new one)
Once a year right about this time, when little bugs have accumulated from all my poking around. This time it was primarily an excuse to move to Win7 from XP.
I reintalled my OS about once a year. I was doing this with Windows XP, and i might keep doing it with Windows 7.
This way it can get rid of problems that annoy me but do not effect the OS operations. It also gives me a chance to "clean house" of files and programs that i no longer use. It also gets rid of any leftover files that might get missed after i uninstall something. You might be suprised a how many files are still left behind after an unintall. Most are hidden deep within the registry, and normally would end up causing more problems manually removing them
Also, i have noticed that many downloaded programs off the interent may not allways be kept up to date. This way i re-downloaded everything i use and normally get the most recent version.