As an illustration to show just how diminishing momentum pressures have become to affect the upward bias of this rally, here is a series of hourly charts of the SPX since 2003. What I am highlighting in the series is the MACD histogram on the hourly chart that expresses itself - almost like the signature of a heart rate on an EKG. During a sustained trend, it oscillates between positive and negative with pulses of momentum and volatility. The closest momentum parallel with today, would be in early 2010 - right after the first round of quantitative easing expired at the end of Q1.
To get a better view - click on the respective chart. They are all of the same scale.