S&P has best month in 9 years

The S&P 500, the most accurate barometer of the market, had its biggest monthly gain since 2000.

The benchmark index soared 9.4 percent in April as many companies reported better-than-expected earnings, lifting the spirits of investors decimated by the never-ending financial crisis. Companies ranging from Wells Fargo & Co. (WFC) to International Business Machines Corp. (IBM) to Ford Motor Co. (F) issued results that surpassed Wall Street's admittedly low expectations.

Investors might giggle with glee knowing that the benchmark index for U.S. stocks must rise only a few more percent points to erase its 2009 loss. But some experts are urging caution.