1. I almost never say "on your left" or anything similar. If there's room to pass and it looks like the passee will hold their line, I'll pass without a word. If there's a bunch of people blocking the whole path, I usually shift from the big ring to the small ring which makes a loud noise and they look back, otherwise I say "excuse me." Every time I've tried "on your left" it just made things worse. Check this out (from http://featuresblogs.chicagotribune....m-passing.html):

"'I never warn anybody when I pass them, because that gives them enough warning to jump out in front and get nailed,' he wrote '(People) hear 'on your left!' and then move to their left! Better just to slip by and be out of the way before they know it."

"He has a point; by the time you hear an 'on your left' it's too late to really do anything. I've seen plenty of startled riders swerve in the wrong direction. And the announcement often sounds rude, like 'get out of my way!'"

2. Pass at whatever speed you want. If you're passing or being passed slowly, say hello.

3. No headphones, it's just too dangerous. Runners/walkers are about the only people who can get away with wearing them because they're only going about 7-8mph tops but even they shouldn't because they need to be aware of what's coming up behind them too so they don't come to a dead stop right in front of a rollerblader or cyclist or whatever.