Re-install all your Debian/Ubuntu Linux apps after upgrade or machine move

Before nuking the old machine
dpkg --get-selections | grep -v deinstall > dpkg-selections
tar czfv etc-apt.tgz /etc/apt dpkg-selections (copy etc-apt.tgz to another machine or usb)

After Reinstall/upgrade OS
untar etc/apt and copy back to /etc
tar xzfv etc-apt.tgz
(NOTE: if you are upgrading, replace the old build for the new build in sources and in source-list.d. ie: replace karmic with lucid, if you do this some apps may not install specially any ppa's you've added)
apt-get update
dpkg --set-selections < dpkg-selections
apt-get apt-get dselect-upgrade