To collectively respond to some points above about it not being the fault of DRS, but that of the Umpires.
First off, the Umpires are part of DRS, and very much a part of the system. The DRS doesnt work independant of the umpires. Ultimately its the umpires who have to adjudicate based on the evidence that the tech presents. So even if the tech works perfectly but the umpires dont know how to interpret that data, its still a failed system overall. Picture sending a misison to another planet, which works great, and send back lots of interesting data, but the scientists have no idea how to interpret that data, then what use is the mission. Its still a total failure.
Same with DRS. Whether it is the tech that fails, or the umpires, who fail to interpret the data correctly or even more appallingly fail to even know the rules about what happens once a review is invoked, its still a failure of the system.
There is an overall system in place, which comprises of both tech and umpires. If either fails, the overall system still fails. Before putting this system in place, first make sure that everyone knows what they are doing !!
Thats the mere min. one would expect. ICC cannot make it up as they go along. Its the World Fking Cup.