In the recent images, starting the 20130813.1, you will notice that click packages have started to show up on the built images. That is, from a user perspective you would probably not notice at all, but if you dive into the system, you will.
Currently, all the packages for the Core Community Apps are being built as click packages, as these are the easiest since are binary independent.
The click packages are built on jenkins, you can take a look at the sudoku-app. These are built in some dynamic form with a click-readiness.py tool that basically reads out the current debian packaging from the sources and builds out a manifest and puts everything in a staged location on which we just run click build.
Since there is no concept of a PPA for a click package they are provisioned on one of the Canonical Servers that can be found here.
While all of the click packages could be installed on the image, we are only installing 3:
The installation is done from a hook in livecd-rootfs which installs them as the phablet user in order for you to enjoy them on the install.
When you install a click package you need to target a user, a click package with no hooks would just lay it out plainly. A click package manifest with hooks will trigger certain actions upon installation, today there are two important ones:
To see the click packages installed for your user (phablet), just run click list. If you want to see the manifests for these click packages just run click list --manifest