Well, there are several major reasons why we cannot build transporters today. One being the question of whether we send the actual atoms or just the information needed to recreate an object. The other major problem that stands between us and a working transporter is Heisenberg’s Principle of Uncertainty. This principle is the easiest to understand, so let’s start there.
     In essence Heisenberg's Principle of Uncertainty says that it is impossible to measure anything with high accuracy because when you make a measurement, you alter the thing you are trying to measure. For us this means that you can measure the Energy State of an atom with high precision but you can’t be sure how long it will stay in that state. To put it another way, one can measure the speed of a particle but you will not know its position and vice versa. Since the act of measuring an object changes the object in some way, it is impossible to create a working transporter today.
     For the moment lets say that you could find a way past Heisenberg then you’d have to deal with the problem of what to do with the actual matter. You could send either the actual object or a copy of the object. If you send the copy then you have to dispose of the original somehow.  But, what are you going to do with it? Maybe turn it into energy but that is for another time.  If we send the matter, then we don’t have to worry about the copy.  Then, you got to worry about sending the matter.  What if you lose some matter?  The subject might lose an arm or something.
     These are some of the problems.  We hope these problems will be overcome in the future and we can travel from New York to San Francisco in a few seconds.