Just to clarify --- 50% retracement is not a Fib number but as you say most people who use Fibs do include the 50% because so many people do look at it. Rejection of a Fib number (or 50%) is a great way to reenter a trend in process.50% retracement definitely works from what I've observed. Not so much because it has any merit on its own, but so many traders follow it like a mantra. I can't say the same for other Fib levels though.