One of the biggest hindrances to power and vertical bar speed is the early arm bend.  For those of you who struggle with bending the arms early, you know the pain this bad habit is.  Bending the arms in the snatch OR clean before the bar has reached maximal speed only slows the bar down and changes the bar track.
Here are two videos of a lifter bending his arms early in a snatch.  First is full speed and the second is my analysis.
Full Speed
What you will notice in these videos is the lifter bends his arms significantly and thus hinders his lift.  Once his arms bend he struggles to remain in the first pull with his heels on the ground.  This is because he has now taken the pressure out of his legs and tried to apply power to the bar with his arms.  Secondly, you will notice that because his arms are bent he does not have the ability to apply power vertically to the bar.  If he did apply vertical power, his arms would just straighten back out and he would achieve nothing.  So to compensate for that inability, he moves his hips horizontally into the bar and over-rotates his shoulders behind the bar which causes the bar to swing out in front of him.  It all began when he bent his arms early.
At this point some of you are watching this video and seeing yourself in the mirror.  You want to know how to fix it.  To be short, the way to fix bad habits is ALWAYS perfect repetitions regardless of weight.  However there are also two lifts that tend to make a lasting impact on this bad habit.  The Tall Snatch/Tall Clean are hugely effective as you have no time to bend your arms and are forced to drive hard into the second pull with your shoulders and hips.  Furthermore, mixing in pulls with your lifts has a huge impact.  What I mean by this is performing a combo where you do a snatch or clean pull for 1-2 reps with perfectly straight arms then perform the full movement trying to mimic the pulls.  Example (ignore the start position).  This combo will create the proper movement pattern with your arms before completing the full movement.
Bottomline, the early arm bend is a power killer and for most will take 10-20kg off your potential.
Oh and this is just awesome… Lindsey Valenzuela Clean Ladder from OC Throwdown