It depends on the situation. If I'm descending fast downhill at 25+, I don't pass, even if there's room. Too much can go wrong. I also don't want to scare the other rider. If it's uphill at a slow speed and I know it'll take me a few seconds to pass, I'll just say "on your left", somewhat quietly so I don't startle the rider. If we're moving on the straights at a decent clip, and there's a lot of clearance, I'll just go wide left, 3 or 4', and not say anything. If there's too much traffic to do that then I'll go with the standard, "on your left", when I'm 5' back and wait for a acknowledgement before making my move.