Quote from Specterx:
Based on the Tuco records, 84% of traders lose, 13% break even or make a little, about 3% make some decent coin.
http://www.elitetrader.com/vb/showthread.php?s=&threadid=162253
As to "fail in the first 6 months," who knows. Depends on your definition of failure. I can imagine that a lot of folks play around in the markets for a few weeks or months, get burned and never touch it again. The long-term success rate is more interesting/important IMO.