Personally, I find their predictive value (in terms of accuracy) to be overrated: a significant problem being that if several lines are being plotted, at which one will price actually reverse? However, when trading pullbacks in trends, I have learned that many retracements occur somewhere between the 38.2 and 61.8 levels, hence I use them as a rough estimate in placing orders, specifically if there is a suitable candle pattern (hammer/shooting star, railway tracks, engulfing pattern, morning/evening star, etc) straddling, or very near to, the retracement level. http://www.forexfactory.com/showthread.php?t=39955