These washes are supposed to remove pesticides, waxes and "people handling residues" (Love that last one!) that water alone cannot remove.
A professor of food science from the University of Maine "studied Fit and found that it was no better than distilled water at cleaning fruit." Normal tap water is fine for cleaning produce, the scientist says. The FDA and The University of Maine also say that washing produce under running water is sufficient.
Those who insist on a special veggie wash have found ways to make less expensive washes using dish soap or baking soda. The Times article says that "anyone worries about getting produce extra clean can also use a mixture of lemon juice and water."