On-line trading has taken off with a vengeance, with an estimated 3 million e-accounts now up and running -- and that number is expected to grow to 14 million in the next five years. Why this sudden surge toward the Internet? Just ask those investors who -- sometimes against all logic -- can't stop trading. Notes one enthusiast: "At eight bucks a pop, you canšt afford not to."

Plus: SmartMoney rates the on-line brokers.