One of my personal pet peeves in both written and spoken English is the confusion of the words "less" and "fewer." These words are not interchangeable. While they have the same essential meaning, one must use them in different contexts.
"Less" applies to quantities that cannot be counted. Less sugar, less air, less dirt, less dust, less light, less water.
"Fewer" applies to quantities that can be counted. Fewer people, fewer aardvarks, fewer tissues, fewer cups.
At the same time, remember: Fewer granules of sugar, fewer molecules of air, fewer dust bunnies, fewer drops of water.