[Hack&Lube]

I never reformat. I only install new versions of Windows (and usually save the old one on a separate drive or partition so I can still access it).

If you know what you are doing and do good maintenance, a windows install can last forever. I usually get attached to one because I have completely modified many aspects of it where it would be painful to try to duplicate that on a fresh install.

I will resort to loading backed up registry hives, copying files from a second windows install, and replacing all the parts of the OS (if it bluescreens on boot) I can manually to save it before I will ever thing about a format. Even doing all that would take much less time than it does for me to create an environment that I am happy with using on a daily basis.

I have Windows 7 on my Sandy Bridge laptops but my desktop machine is used mainly for music production and most of my software licenses are for XP. That install has been with me for over 10 years, since XP came out. It's been cloned and moved from harddrive to harddrive from an Athlon XP system (VIA) to an Athlon 64 (NF3) to an Opteron to an Athlon X2 (NF4), and finally to a Intel socket 775 (P45) chipset. People always say to reformat when moving between motherboards but I have never done it. I just install the drivers manually, even when changing between something completely different. It does work!

To be honest, I'll probably never do this sort of thing again but it's worth it for me for the amount of changes and software I have installed and modifed on this particular XP installation that I cannot replace.

I just use Acronis images and VMware now though for easy backups and running OS's that you can allow to screw up without affecting your whole system. To be honest, computers are fast enough with new CPU architectures and SSDs that you can run all your OS's as virtualizations and so if there are ever any problems, it is extremely easy to deal with and it will rarely ever affect the overall system.

Do what Sclitheroe said and instead of wasting time on formatting, reinstalling Windows, reinstalling all your programs, downloading all the updates, making all the changes to the OS, making all the profiles, importing all your files, mail, settings, etc. Just make a backup image once a month. It will save you all the time in the world.

What Sclitheroe said is true, the clogged up registry or extra dlls and extra hidden files do not slow your system down. It's just how you manage the system properly. Extra files can cause the indexing service to slow down (turn it off then) but any services and installed programs that have been installed and run at boot or in the background can be simply checked and deactivated or uninstalled. That's basically it for things that can actually slow down your PC aside from a fragmented mechanical drive or simply buggy software.