What's the difference between Haineko and Senbonzakura? What's the difference between these two shikai; Rangiku's Haineko and Byakuya's Senbonzakura? They both seem to have the same abilities.
For Matsumoto Rangiku's shikai:


  When released with the command "growl" (唸れ unare?), the blade dissolves into ash. In combat, Matsumoto can control the movement of the ash, and cut anything it lands on by moving the hilt. The ash is also solid enough to be used as a shield to block enemy attacks


For Kuchiki Byakuya's shikai:


  ...Senbonzakura's blade separates into thousands of slender, petal-like blades.... While the blades are too small to be seen by the naked eye, they reflect light in such a way as to appear as cherry blossom petals. Byakuya can control the blades at will thereby allowing him to shred opponents at a distance and break through almost any defense. While Byakuya can control the blades with his mind alone, using his hands allows him to do so more effectively, making the blades move twice as fast.


There seem to be a few main differences, though they are very similar. 


Byakuya can control the blades of his with his mind, while Matsumoto needs to move the hilt.
The ash can be used as a shield while Senbonzakura cannot.