My dropshot is pretty hit-or-miss; either it will go over and be ungettable or it will just plop into the net on my side.
The problem is I try to use it far too much. If I am in a baseline rally that goes on for more than four shots, I will just get frustrated and try a drop. Or if I am playing someone really good and trying to find a way to beat them, I will hit a load of dropshots (and usually miss). Sometimes when I am under pressure in a point, I will try to hit one. But the most effective use is when my opponent is at the net, and I'm not in a position to pass or lob, so I just hit a low floater of a drop shot at them which gives me loads of time to recover. They are usually so surprised that they hit a weak volley which I chase down and smack for a winner.