Oh, an older thread but one well worth bumping back up.
Personally, I've made it fairly clear when asked that I don't believe in what I sometimes view as an "undue" amount of formality to my D/s. But collars are, for me, the exception.
I take collars very seriously. I would never put on someone's collar if I was less than dead serious about it, personally. Nor would I collar anyone lightly. It's hard to explain why, but collars were actually the first D/s symbol of some sort that I can remember really "identifying" with in my early 20's, and they still have a fairly large effect on me.
To me personally, my collar is the symbol of my bond, my contract such as it exists, our love, our mutual respect, our trust, and my gift of service, as well as Her acceptance of that gift and the responsibility that comes with it.
So for me personally, I choose to put collars in a position where they hold a lot of meaning and are much more than a casual toy. If some choose to express those things in other ways, that's fine too.But for me a collar is the symbol and formality of choice.