I have kept a bell on my little girl from the day i got her as a 8 week old furball. She hated it at first but got use to it. As so did I, I dont notice it at all. It is quite convenient to call her name when i havent seen her for a little while. I only need to hear it jingle once and i know exactly where she is.
My cats don't have collars, but growing up, the family cat had a bell on her collar and I liked being able to find her and it was cute to hear the bell ringing as she came running to us. If I were to use a collar now, though, I probably would not use a bell because it has to stink to ring all the time....and I had never thought (until I read this thread) about how easy it makes it for predators if the cat would get outside.