With the economy still sluggish and the jobless rate stuck at 7.8%, the S&P 500 is showing only modest gains in the fourth-quarter earnings season. Reports are in from nearly 30% of the companies in the index. S&P 500 earnings now are expected to rise 2.8% vs. Q4 2011, according to Thomson Reuters. That's better than Q3's anemic 0.1%, but down from the 8% to 9% growth seen in the prior three quarters. Apple (AAPL) used to provide a notable boost