I gave up "on your left" years ago as well, especially for walkers. Many people hear the word "left" and move left.

Now I pass people by one of two methods. If I'm going to pass relatively close to someone, where they may get startled, I slow down to near their speed (even if they're walking) and say "pardon me" as I ease around them. I'm usually biking for exercise when I'm riding at speed. A certain amount of braking and subsequent acceleration breaks up the monotony and adds to the workout.

If there's plenty of room, I move over and glide past them at speed with my fingers on my brakes for any emergency slowdown. Coasting past someone isn't as startling as furiously pedaling like I'm trying to beat them to the finish line.