dafalax,
Here is something I use to help me understand the difference between “Tradition” (Sacred or Apostolic Tradition) and traditions (such as the dates we celebrate Mary’s birth or even Christ’s birthday).
The rule I use is “Tradition” is that which is found and proclaimed in our Creeds, our Liturgy and in the Sacraments. These are the truths of the faith given to us by the Apostles and through the “Sacred Tradition” and cannot change. These are the essentials truths of our Faith. All the dogmas of the Church are based on these truths. This (and I am using the singular form on purpose) and all the Doctrines of the Church are simply (that is purely) the teachings of the Church which embodies and explains these truths.
Traditions, with a small “T” are the ways we have, over the course of the years celebrated, these unchanging truths and are not essential in themselves and thus can change, with time, if the Church, in Her wisdom which is guided by the Holy Spirit, comes to understand that certain tradition need to be change and updated to alow her to better acomplish her God given role to proclaim the Gospel Message and to fulfill her Sacramental Role in the world in which we live. (But here I cannot stress enough it is the Church’s right and duty to make these “Accidental” changes not individuals or groups of individuals).
Hopefully this will help a little, but again the best way to understand “Tradition” is to know our Creeds and celebrate our Sacraments.