Rarely needed it until I discovered canal commuting about two months ago. Adds about 2½ miles to my journey, but hey, no motor traffic, no traffic lights etc.
Mind you, so many people are plugged into iPods these days, they just don't hear you.
Off topic - the canal route is going to become unusable after about this week, because it's going to get too dark to use safely. I started because post-Olympics the roads have become insane. My perception is that they are now busier than ever - is this others' experience, too, I wonder?
Tbh, I'm dreading having to go back to road commuting again.
I just shout at people if they don't hear me. I do the usual "Excuse me, Please" a few times and if they have headphones in or are ignoring me (Have had it happen!) I raise my voice. I know it looks rude but if they can't hear me what am I supposed to do? Sit there until they notice me?
I had a girl once cross the road as I was turning into the corner (going too quick to stop, if I'd braked i'd have come off and hit her anyway. Didn't think she'd walk without looking which is exactly what she did....) and I screamed at her to stop. She did thankfully because 16st of human and 11kg of bike generally make a mess of a teenage girl who doesn't look. Had a hood up, didn't look. Moron.
I had another pair of school girls walk at me on a shared use path (Narrow enough so I couldn't pass them). They were both plugged into their iPods staring at their phones. I ended up stopping and they walked straight into me as I told them to stop repeatedly. Lights on, hi-viz, the lot.
Bells don't work. Voices work better.