Also, I realize I could be a nuisance to others on the trails, especially hikers and slower riders. On certain trials, I use a small bell to warn others. Most of my ride buddies laugh at the bell, but I feel the good will a simple "ding" to warn others is well worth it. I've had hikers thank me for sounding the bell. I'm sure hikers get startled when a rider passes them without warning. Some riders yell "on your left", but they always sound like cops barking out orders.
I also use the bell on tight single tracks when I can hear a rider approaching on a blind turn. Since I'm usually riding point on ascents, I rib my ride partners that if they were ever first up the hill, they'd want a bell too.