I've talked about it before, actually. I'll track that down later.
Here's a definition of shibboleth. I have to say that I don't like definitions 2 and 3; they seem more like ignorant misuses than I care to see. Notice that the examples are all of those 2. There must be better words for what they're trying to say.
Amusingly, I'm using the word in a fashion similar to the Gileadites. (Well...no actual bloodshed... Yet.) For more on that, check this article.
I seem to be fascinated by [or hung-up on] this story and this word. I guess I can see how shibboleths can be useful, when used with care... but they, 'like fire, are dangerous servants and fearful masters.'