If you are a hard-core Ubuntu fan and keep customizing ubuntu, you're sure be a victim of the loss of customization after a fresh install. You can always recustomize it but its boring and irritating. To solve this problem, you can use YourGnome, a software that can backup your Gnome settings and restore them in ONE SINGLE CLICK. YourGnome is actually a shell script that does all the magic. Its a fantastic project and you can find its home page here - http://code.google.com/p/yourgnome/.
Firefox and Pidgin's settings are yet another important softwares which one would want to have their settings restored. This is again very simple.
To restore firefox settings, just copy the .mozilla folder in home folder of your old installation to the home folder of your new installation. Just replace the existing .mozilla folder. This will do all good and no harm :D
Pidgin configuration restoration is also as simple as for Firefox. Just copy the .purple folder from old install's home folder to the new installation's home folder.