It's often impossible to catch a cab in midtown. I think they need to add still more taxis, and then maybe there wouldn't be such demand for the pedicabs. It seems like everytime I'm standing at an intersection and someone gets in one of these things, it's because they tried unsuccessfully to hail a regular cab. I see how they fill a real need for shorter-distance rides.
Tourists seem to have fun in them as well, taking in sights as they ride along.
That said, I've also seen them swerve dangerously close to cars.