Back in the days of Win9x, I had to re-install fairly often.
Since Win7, I don't re-install very often any more.
Usually, it's because I'm swapping a hard drive to something bigger, or an SSD.
Now, my strategy is:
Have all my documents/pictures etc backed up elsewhere. For some things, like thunderbird, I need to take special precautions to ensure I have it's working directory backed up, and know how to restore it to a new install.
Remove all partitions on the disk, and re-install on bare metal.
Add programs only as they become necessary. So I will install Office straight away, and other things I use every day: Filezilla. Garmin Mapsource and all my maps. Notepad++. etc, etc
Other stuff is installed as and when it's needed; I don't try to re-create my old setup from the get-go.