Although when it comes to taking backups, if you know your way around, then they are again very useful. But if you want to backup and automatically create a .iso CD/DVD image of your downloaded packages (after installing Ubuntu or anything distro that supports those application managers) by using another app that has an easy to use GUI, then you should try APTonCD!.
For all the beginners, with all the due respect, let me point out the benefit of this app.
Say that you installed multimedia codes in Ubuntu (in your PC) and with the help of this app, you can manually copy those packages (codes and all that) to a CD/DVD thus creating a portable repository that can be used to install those multimedia codecs in a PC where an internet connection is absent!. So, by using this tool, in that case, you can easily create an offline codec portable codec pack!, how's that for a inspiration :P.
So, as usual, open your Terminal and issue the below command to install APTonCD in Ubuntu 10.10 (should work on earlier ones as well).
sudo apt-get install aptoncd