Below is a chart showing the percentage of stocks trading above their 50-day moving averages on a daily basis going back to the start of 2009. Also included in the chart is the price of the S&P 500 over this same time period.
At the moment, just 76% of stocks in the S&P 500 are above their 50-days, even with the index itself trading at bull market highs. Breadth hasn't nearly gotten up to the levels it normally gets to when the market has been as overbought as it is now in the past. As shown in the chart, readings in the 90s have been common throughout this bull market, but the high we've seen in 2012 as the market has surged has been 87%.
Bulls can make a case that weak breadth means there's more room to run for this rally, but bears probably have the upper hand with the argument that this rally has seen less stock participation than normal.