I am in the midst of reading To Pray As a Jew. It is interesting how the line between law and tradition tends to be blurred in Judaism.
A good example is tefillin. The Torah commands one to bind the words to one's head and one's arm. That's fine. But, through Rabbinical discourse in the Talmud, one is now commanded to put on tefillin every morning, except on Shabbos and a few other days.
How do we know that G-d commanded us to do it only once in our lifetime, as opposed to daily?
I am not one who tries to throw tradition out the window. I completely understand the value of traditions. My concern with religion has always been that customs become synonymous with Biblical law. These blurred lines are not healthy for any system, and can result in unnecessary zealotry.
Another example - wearing a kippa. There is no religious law telling a man to conver his head when he enters synagogue. It is simply a tradition to show respect for G-d. That's great. But, try stepping into a synagogue without a head covering and pay attention to the looks you receive. Some will look on in great discomfort because one chooses not to. For some, this discomfort comes from someone doing something different, but others might actually believe G-d commanded men to wear kippot.
Where is the checks and balance for these things?