Carolina,
It really depends upon what your needs are.
You can apply effectivity to track serial configurations, however if you need to track specific Serialized units that falls under Product Instance capabilities.
We are working on adding to the Help content on Effectivity and you should see some updates in the M030 and more planned for the future.
In terms of the DS/CI pattern discussed above - that is part of the Windchill Aerospace and Defense module and really geared towards aircraft design.
In 2010 I gave a session covering Effectivity - its missing from the PTC/USER library - I am having it added, but am attaching to this reply
Additionally I am attaching another file showing examples of Effectivity basics & propagation
In 2012 at PTC Live I gave a session on Configuration Management that included Product Instances - it can be found on the PTC/USER site in the Library - here is a link to that - http://portal.ptcuser.org/p/do/sd/sid=2010&fid=1458&req=direct