most important for me are my quicklists, launchers etc that I made once and transfer to every new installation.
furthermore edit my fstab file to mount my NAS automatically,
install synaptic (!), (G)rsync
compiz settings manager/gnome tweak/faenza icons
dropbox and a loooooong list of other applications.
used to have a lot of work in the old days (pre- Linux).Now, thanks to synaptic and a good "script", less then two hours!