Wouldnt say they are rare but can occur on stocks only a few times a year. Last time SKTO had it was March 11 and AEGY in May when the stocks skyrocketed. Usually occur when stocks have been on a bullish uptrend for a while or when some great news occurs, its more like a confirmation of the uptrend. Stock is pretty much self-marketing itself with a crossover, people see it as a company on the upswing and even MM's tend to lighten up a bit on the shorting till it peaks. Many traders look for Golden Crosses, its the most popular sign of a bullish stock