If you're only updating one machine over the Internet, then upgrades via the repositories are a necessary evil. But do you really need to waste all that bandwidth downloading the same packages over and over again for all your machines?
The answer to this problem is APTonCD. You update one machine, after which you run APTonCD on it. APTonCD will compile all the packages you've downloaded (stored in
/var/cache/apt/archives) and turn it into a local repository CD.
When you plug the repository CD into another Ubuntu machine, it will automatically start Synaptic. From there you can update your machine without having to download the packages again.
This also works great for sharing update repositories with friends who may not have a broadband connection.
Instructions and screenshots follow.
First, install APTonCD from the repositories (while you're online, naturally):
sudo apt-get install aptoncd
Then, run APTonCD, either via the command line or from the System menu of the main Ubuntu menu bar. This will bring up the wizard. From here on, everything else is pretty much intuitive.
The end result is an ISO file. When burned to CD, it will have the following structure.