I don't like the challenge system. Rather, I agree with Mary Carillo that players should have the right to challenge line calls whenever they wish. The last accuracy numbers that were compiled for linespeople at WTA and ATP matches (or at least, the last numbers I saw) revealed that the line callers were correct 70% of the time. I remember Pam Shriver saying how "great" that was, and all I could think of was: What would happen to me professionally if my work was correct only 70% of the time? 70% is far from "great."
Then there is the matter of Hawk-Eye's absence on clay courts. Because the ball leaves a mark in the clay, the chair umpire is still called upon, if necessasry, to check the mark and determine whether the line caller was accurate in her call. There are problems with this system, however, and the main one is that after a match has been underway for a while, there are many marks in the clay. This year in Charleston, for example, the crowd yelled "Wrong mark!" at a chair umpire, who proceeded to call the line based on the wrong mark. I have seen this happen before.
We have an active clay season, which culminates with the French Open. Is it time to install Hawk-Eye?