Your Mutual Fund Doesn't Return as Much as You Think by: ARA Content(ARA) - As tax time nears, many mutual fund investors are starting to wince. While most mutual funds' returns were down last year, their tax bill remains high.After years under-performing the S&P 500, the average US stock mutual fund finally beat the index last year. But while the average fund was down just 0.37% v. the S&P 500's