Agreed with what some others have said. Those claiming you can get a double digit return are probably referring to the last 5 years, when the dow was trading in the 7,000-8,000 point range and rode a great bull market. The historical average is somewhere between 7%-9% range, and that is if you invest in the one of the indexes (DJIA, S&P, etc). You can try and beat the market by investing in certain companies as opposed to an index or mutual fund, but you may not beat the market that way.
The way the market looks now, the bull run may be cooling off and could get back to a more historical normal. We could end the year on a lower note, the first time in over 5 years.