There are constant rumblings from many of the trading blogs regarding the underlying internal weakness accompanying the incessant rise of the US stock market since March of 2009, and especially since July 2010.  The explanation for this may may be as simple as one of the Elliott Wave guidelines of wave personality:  fifth waves are by nature, weaker in breadth than third waves. 
The above chart is strictly “food for thought”, by the way.  I’m not at all convinced that the above depiction is the way this story will unfold, primarily because some of the internal wave behavior of the upward move since March ’09 just isn’t cleanly impulsive.  There are overlapping areas in the middle of what must be counted as 3rd waves that really shouldn’t be there.  One thing that can be stated with certainty, this melt-up since March ’09, whatever the count, has displayed absolutely remarkable “lift”.  The trend is most assuredly UP for now . .