At least for programs usage. A re-format re-install of windows (even XP and
2k) is considered making the system "cleaner," and is adviced when
benchmarking hardware performance.
As you install and uninstall programs, they usually don't remove what they
wrote to the registry.
Therefore I love programs that you don't need to re-install and everything
"is there" just double-click the .exe file after a re-format and re-install.
Saves time too, but few care more about their customers then their ability
to spend money.
A few programs that's "idealistic:"
http://jooh.no/prog_parasitic.html
http://jooh.no/prog_trillian.html
I just reinstalled XP and went into d:\prografile\trillian\trillian and ran
trillian.exe: all my settings, contacts and chat history where there (stored
in d:\prografile\trillian\gambler). I clicked "load trillian at startup" and
I could msg my friends to say "im back!"