Dpsyco introduces the concept of configuration packages. It is a special form of debian packages that is applied on top of the original debian packages. With this you can add users, groups, apply a file skeleton, patch things and more. Observe! No such configuration packages should be uploaded to the debian archives. This kind of things are intended to be created and used by the system administrator only.
For more information see http://www.opal.dhs.org/programs/dpsyco/.
This tool is very useful if you have a lot of servers on which you want to have similar configuration (but not identical). If you only have one server (or client) this is probably not useful at all.
WARNING! Users with UID and GID between 500 and 999 will be automatically administrated by this tool. This means that if you do not have a admin package that set up users these users WILL BE REMOVED. Groups with GID between 300 and 499 will be handled in the same way. YOU HAVE BEEN WARNED!